They finally had a lead, the brothers were so happy and they wasted no time in going back to the Underground. They needed to get into that room in Waterfall but first they needed the time machine and the DT Extractor. They went to the lab in Hotland first to get them, since Sans had moved his machine there for safe keeping after Frisk freed them. Both of the skelebros were feeling more hopeful than ever before.

Sans knew there was something he was missing but he tried not to worry about it. There was no one left in the Underground so they were free to just walk into the lab and take what they needed. As Frisk and Papyrus began gathering equipment and tools that had been left behind, Sans found himself wandering and thinking back to what his father had said to him when he was dying last reset.

He stood outside his father's old office, only Sans had a key to it so no one else had entered since Gaster disappeared. Sans knew there was nothing there, he'd searched the office so many times but he still found himself unlocking the door and going in. He had so many memories in the office, he and Papyrus used to play there all the time while their father worked, Sans used to help him with his work as much as he could. Now the office was dusty and unused. Sans sighed and turned on the light before going over to the desk and sitting in his father's chair. He proceeded to spin on it. Once he got dizzy he stopped and rested his elbows on the desk, head in his hands.

"what am i even doing?" Sans muttered to himself, "it's just going to end up as another dead end..."

Sans found himself looking around the room, eyes finally settling on the old bookcase in the corner. He got up and walked towards it, there was something about it that made him think there was an answer somewhere in there but he'd been through every book, he knew there was nothing. Behind the bookcase... Sans frowned, his father had said something about there being something behind the bookcase...

"HEY SANS! WHAT ARE YOU DOING HERE? WE HAVE THE STUFF, NOW WE NEED TO TELEPORT TO WATERFALL," Papyrus said as he ran into the room, he was clearly excited, he really belived that this would be it. Frisk was following closely behind him.

"hey, help me move this bookcase." Sans didn't take his eyes off of it.

"WHY?"

"just do it."

Papyrus and Frisk looked at each other and shrugged. They didn't know why he wanted to move it but there was no harm in doing so. The three of the took hold of the bookcase, Papyrus pulled while Sans and Frisk pushed. With the three of them working together it moved rather easily.

"OH WOWIE! THERE'S A SAFE THERE!" Papyrus said. The safe was flush against the fall, it looked brand-new and shiny, it really stood out in the old fashioned, dirty office.

Sans nodded, "i think there might be something to help us in there."

"Okay, so lets open it," Frisk said as they stepped forward, "what's the combination?"

They both looked at Sans expectantly but Sans only shrugged. "no idea, let's just guess."

"YOU DON'T KNOW?! WHAT WOULD WE EVEN GUESS?" Papyrus huffed.

Sans shrugged again and looked at the safe a little closer, "it's four digits, lets try dates? ...lets see... dad's birthday... nope... asgore's maybe... nope... grillby's... nope."

Papyrus pushed Sans out of the way, "IF IT'S DAD'S SAFE LET'S TRY OURS! MINE FIRST," Papyrus typed in his own birthday, it didn't work, "YOURS THEN." That didn't work either.

Sans pushed his brother back out of the way. "maybe it's not a birthday. lets try dad's bankcard's pin number!" Sans typed that in, it didn't work.

"HOW DO YOU KNOW DAD'S PIN NUMBER?" Papyrus asked.

"oh, i just watched as he typed it in when we went shopping and then when i learned to shortcut, i stole it and went to grillby's. the old man spend so much money on us i don't think he never noticed when he got the bank statement and grillby never thought it was weird since dad spoilt us so much, he just thought i had permission."

Papyrus didn't look angry at his brother's thieving and addiction to greasy food, just disappointed. "SANS, YOU ARE TERRIBLE!"

"heh, i know."

Frisk, curious about what was in the safe and desperate to get to work, pushed past the brothers and typed in '0000' that, to, did not work, they went on and typed in '0001.' "Let's just type in everything in order. We'll get there eventually."

"that'll take too long," Sans said, "i'm sure we can figure it out."

"You two can figure it out, after all I never knew him. While you guys talk it over I'll keep doing this. It might just be random."

"THAT SOUNDS LIKE A PLAN! IS THERE ANY OTHER DATES YOU WANT TO TRY, SANS?"

Sans shook his head, "i can't think of any, i don't think it's a birthday..."

Papyrus put his hand to his chin in thought. "MAYBE IT IS. WE WERE BORN IN THE SAME MONTH, ALTHOUGH SEVEN YEARS APART, SO WHY DON'T WE TRY THE DAYS OF BOTH OF OURS."

Sans shrugged, "might as well."

Frisk got out of the way and let Sans type in the numbers, it opened, inside there were several files and some machine parts. Frisk curiously picked up a very thick file, they couldn't read the title as it was in wingdings so they just opened it to a random page.

"Aww, Sans you were so cute as a baby!" They cooed and held the file open and showed the brothers the photos of baby Sans that were glued in. He was dressed in a panda onesie and holding on tightly to a ketchup bottle, a few pictures had Gaster's hands in them, it looked like he was trying to take the bottle away but Sans seemed to be holding on too tightly.

"oh my god, give me that!" Sans said he as snatched the file from Frisk.

"AWW BROTHER, ARE YOU EMBARRASSED~?" Papyrus teased as he leaned over trying to see the file that Sans was holding to his chest to stop him from looking.

"shut up!"

Papyrus shrugged and went into the safe, "OH LOOK HERE'S MINE!" He said as he pulled out another file and handing it to Frisk, "UNLIKE MY BROTHER I DON'T MIND YOU LOOKING AT MY BABY PICTURES!"

Sans rolled his eyes as his brother and friend began to look through the pictures and journal entries. Frisk was asking questions about how Sans and Papyrus came into being when they saw the little soul in the tube. Sans just couldn't believe that out of all the research and important work his father had done in his life the things he kept hidden and safe where their records and baby pictures. There was another file inside the safe however, Gaster's DT and space/time travel research; that was what Sans needed. He finally read the other sixteen entries he never had and he had the complete blueprints for the machine as well as all the missing parts. He finally had all the things he needed to free him and it had been here all along. He wished he could've gotten to it sooner but he was happy he was finally going to do it, finally after fourteen years, he'd have his dad back.

It took them a long time and a lot of teleportation to find the room Frisk spoke of but they found it eventually.

Papyrus looked at the out of place grey door and took his brother's hand. "IS THIS REALLY IT?"

Sans nodded, "let's do this."

Frisk, happy to have finally found it, rushed over and opened the door. The three of them stepped inside...

The room was empty and cold but they didn't let that deter them as they began to set up the time machine and the smaller DT Extractor.

"SANS THIS WILL WORK RIGHT? WE WON'T BE TORN APART? WE'LL BRING HIM BACK?"

"don't worry, bro, i've modified the machine with alphys and with dad's notes and parts it can't fail."

"What will the machine do?" Frisk asked looking at it.

"it'll pull him back together, he was shattered into pieces and most of them seem to gather here. once we've done that paps and i will have to pull him out of the void with blue magic. then we'll get the DT out of him and hope he hasn't gotten madder. we will have to be careful to get the right gaster though."

Papyrus frowned, "WHAT DO YOU MEAN 'GET THE RIGHT GASTER?'"

"multiverse, bro. there are hundreds, no, thousands of alternate universes, we don't want to accidentally get the wrong one, one that might be evil or abusive or something. we have to get our dad. i think that's what river was warning us about."

Papyrus was nervous enough as it was but he nodded anyway. No matter how scared he was, he wanted his dad back more than anything. "SO WHAT'S THE PLAN? YOU FIRE UP THE MACHINE WE BOTH PULL HIM OUT AND PUSH HIM INTO THE EXTRACTOR AND FRISK TURNS IT ON AND WE GET THE DT OUT OF HIM?"

Sans nodded, "yeah sounds good to me. you alright with that plan kiddo?"

Frisk gave the skelebros a thumbs up and stood next to the Extractor, ready to turn it on the second Gaster was in place.

"right, no time to waste. ready, bro?"

Papyrus pushed his fears aside and forced himself to smile. "THE GREAT PAPYRUS IS ALWAYS READY!" He announced.

Sans gave his brother a reassuring smile and began to type in code. The screen lit up showing millions of little dots. "these dots represent all the peaces of all gasters." Sans explained as he kept typing, "we need to code it so it only pulls together our one."

Papyrus and Frisk watched closely as Sans typed quickly. Slowly all the little dots began to gather together into different clumps. Sans frowned and kept typing, one clump re-shattered.

Papyrus gasped at it. "WAS THAT-"

"don't worry, bro," Sans assured, "that code wasn't from our universe. 'm pretty sure that was the gaster from underfell; he's defiantly evil."

"UNDERFELL?"

"just one of the many universes. trust me bro, we don't wanna mess with that one."

Frisk couldn't help their curiosity. "You seem to know a lot about these universes... Have you been there?"

Sans shook his head, "no, but dad has. he's been to a lot of them. i found a lot of reports where he detailed lots about each one he visited. i didn't want to risk myself trying it, although it is much safer than travelling through time. i also can't really be arsed with it, too much effort."

"LAZY!" Papyrus called out. Frisk laughed and Sans shook his head.

Eventually there was only one clump left. "this's it!" Sans called and Papyrus grabbed Sans's hand again, squeezing tightly.

Everything that happened next happened so fast. Sans typed out a long sequence of code with one hand, the other holding tightly onto Papyrus's. The machine began to rumble and a dark portal opened, it threatened to expand but the machine seemed to keep it small. There was movement inside of it, blobs of something coming together into a goopy mess. The goopy mess soon began to form into a person, a person who was screaming. The second the soul came together the brothers turned it blue and pulled. There was a resistance, something was pulling back but the brothers were stronger than they had been as children. They were stronger and more determined, they were not going to let the Void have their father. Sans and Papyrus help on tightly to each other's hand and pulled harder, they could do it.

"DAD!"

"dad!"

With a final tug the brothers won and their father came stumbling out of the Void and back to reality. They had no time to waste and pushed him into the DT Extractor. Frisk turned it on and Gaster's soul was trapped inside of it. Gaster seemed too dazed to fight it or even realise what was happening, although he did scream out as the DT was removed. The machine did it's job, taking out all the DT and Gaster's body became less goopy and more solid as more was removed until he was normal again.

He was released from the machine and fell forward onto his face on the ground, his clothes were all torn but he was unhurt. Sans and Papyrus let out a sigh of relief and let go of each other, Sans sat on the floor and laughed. "heh heh we did it, we finally did it! it's over!"

"NYEH HEH HEH!" Papyrus laughed with his brother before he took a step forward to help his father up. Neither of them could believe it and they were so happy.

Gaster got up on his own though. The first thing he noticed was that he was limping again but he payed it no mind and he looked at the three people in front of him.

It was too much, he didn't know where he was. The last thing he knew he was falling and his children were calling for him. He was haunted by memories of other timelines and universes, he'd been trapped for so long and yet no time at all, an eternity but for only a second. He didn't know what was real and what was a hallucination and this looked like freedom, but he couldn't be free; the Void had him and would never let him leave. He decided this wasn't real, he decided this was a hallucination. He decided he had finally snapped and gone truly mad.

Gaster summoned a blaster and fired it at the hallucinations. They weren't real, they couldn't be, he didn't want to see this, he didn't want hope for something that wouldn't happen.

"dad!?" Sans shouted as he dodged.

Gaster sent a series of bone attacks forward.

"SANS? IS THIS ONE OF THE EVIL DADS YOU WERE TALKING ABOUT? LIKE 'UNDERFELL?' DID WE GET THE WRONG ONE?"

Sans shook his head, "this is our dad, i don't know what's going on."

Frisk wasn't going to stand by and watch, they chose ACT then TALK. "Dr Gaster! Stop! We don't want to fight you! Your sons don't want to fight you!"

"THEY'RE NOT MY SONS!" Gaster yelled, two magic hands sighing his words so quickly Frisk barely had time to see what he had said. "THIS IS ALL AN ILLUSION! IT'S NOT REAL! IT CAN'T BE..."

"DAD, PLEASE THIS IS REAL! WE'RE HERE, YOU'RE SAFE!" Papyrus called out.

"MY SONS ARE CHILDREN!" Gaster called as he sent out another bone attack, followed by a blaster.

"no we're not! dad we are here, we freed you. i'm so sorry it took so long!" Sans tried.

Gaster shook his head. Two blasters appeared and fired. "I'M TRAPPED FOREVER! ALONE FOREVER!"

They could only dodge as more attacks came at them, quickly. Frisk chose TALK again, "You aren't trapped. You're free. You don't have to fight anymore. Monster-kind is free!"

"JUST STOP! GO AWAY! WHY MUST YOU TORMENT ME?! I JUST WANT MY FAMILY!"

Despite his obvious limp, Gaster was so fast, his attacks so strong. Frisk was scared, scared that Gaster would kill them, that he'd kill his own children believing they weren't real. They didn't know what to do; talking didn't work and picking mercy wasn't doing anything, Gaster wouldn't accept it.

"JUST LEAVE ME ALONE! IT'S MY FATE TO BE ALONE, THE LAST OF MY KIND... EVERYONE I LOVE IS DEAD..."

Papyrus gasped and grabbed hold of Sans by his hood, dragging him forward, closer to their father. He couldn't take this, he didn't like what he was saying, he wanted it to end.

Papyrus reached out and took his father's right hand, looked him in the eye and said, "DAD, YOU ARE NOT ALONE. SANS AND I ARE HERE. PLEASE COME BACK TO US! WE MISS YOU!"

Gaster flinched and looked at the illusion of his youngest child... Was it not an illusion? He could touch him... You can't touch illusions... He told him he wasn't alone...

Sans took his father left hand and squeezed it, "dad, we're really here. you're free and definitely not alone. i'm so sorry i ever gave up hope."

Gaster looked at both of his sons, they were there, real and in front of him. He felt the tears fall and his legs gave out from under him, he fell to his knees. "MY BOYS..." He sobbed.

The skelebros also fell to their knees refusing to let go of Gaster's hands. Gaster looked down at his hands, that were holding on tight to his sons'. He was solid and no longer goopy, he was back. He felt so guilty that he put his children though that. His guilt only grew when he looked up to his sons and saw that they were clearly no longer children but adults, they were all grown up. He'd missed all of Sans's teenage years and pretty much all of Papyrus's childhood.

"I'M SORRY!" He sobbed out, "OH I'M SO SORRY! WHAT HAVE I DONE?! I'M SORRY... SORRY FOR EVERYTHING!"

The brothers to began to cry. They let go of their father's hands and threw their arms around him. Gaster returned the hug, pulling his sons closer to him as he kept apologising over and over.

Eventually the skeleton family calmed down and let go of each other. Gaster stared at his boys and wiped his tears away, "I'M SORRY," he said again.

"IT'S OKAY!" Papyrus said, "WHAT HAPPENED WASN'T YOUR FAULT! WE'RE SO HAPPY YOU'RE BACK!"

"BUT... I MISSED YOUR WHOLE LIVES! I LEFT YOU ALONE FOR SO LONG. I'M A TERRIBLE FATHER, I SHOULDN'T HAVE-"

"dad, stop. it doesn't matter. what happened, happened. you're back now and we forgive you."

Gaster began to sob again, "MY BOYS, I'M SO PROUD OF YOU. I SWEAR I'LL MAKE IT UP TO YOU, I'LL NEVER LEAVE YOU TWO AGAIN. YOU BOTH MEAN THE WORLD TO ME."

Papyrus stood up and offered a hand to Gaster, "LETS GO HOME, WE'RE LIVING ON THE SURFACE NOW, BY THE WAY."

Gaster gasped as he took his son's hand and pulled himself up. "THE SURFACE? SO DID ASGORE KILL-"

"nope," Sans interrupted again, he stood up as well and pointed at Frisk. "this is frisk, they saved us all."

Gaster looked them up and down, they looked familiar to him but he was forgetting everything he saw in the Void; the world once again fixing itself, Gaster couldn't know anything about what happened when he was lost. He smiled and tried to step forward only to stumble without his cane, luckily Papyrus was there to catch him and allowed Gaster to lean on him as he stepped forward. "IT'S A PLEASURE TO MEET YOU, FRISK," Gaster said as he offered his hand. "I'M DOCTOR WINGDINGS GASTER. PLEASE, JUST CALL ME GASTER."

Frisk smiled as well and took his hand. "Nice to meet you too."

Sans had never been happier, everything was alright, everything was finally normal again. "man, we have so much to catch up on."

Gaster chuckled, "CLEARLY! JUST LOOK AT HOW TALL PAPYRUS IS! MY LITTLE BABY'S GOTTEN SO BIG!"

Papyrus laughed and straightened up. "OF COURSE I'M TALL! YOU ARE AND YOU'RE STILL TALLER THAN ME!"

Gaster shrugged, "THAT'S TRUE BUT YOU'RE STILL SO TALL! AND SANS!" Gaster turned to his oldest and narrowed his eyes, Sans couldn't tell if he was squinting because he couldn't see without his glasses or if he was giving him a dirty look. "...I SEE YOU GOT FAT."

"hey!" Sans said raising his hand to his chest as if wounded, "i'm not fat, just big boned."

"THAT'S THE SAME THING, BROTHER!"

"it is not."

"IT IS FOR SKELETONS! I KEEP TELLING YOU TO GO ON A DIET AND STOP EATING AT GRILLBY'S ALL THE TIME!" Papyrus scolded his older brother.

Gaster laughed as his sons' bickered over greasy food, "I'VE MISSED YOU BOYS SO MUCH!"

"we missed you too."

"...HOW LONG AS IT BEEN?" Gaster dared to ask. "FOR ME IF WAS FOREVER AND AT THE SAME TIME MERELY SECONDS."

The skelebros looked at each other before Papyrus answered, "IT'S BEEN FOURTEEN YEARS."

Papyrus had to tighten his grip as he felt his father almost faint. "FOURTEEN YEARS? THAT'S SO LONG, I'M SO SORRY... OH GOD... MY BABIES ARE ADULTS..."

"this must be pretty weird huh?" Sans asked. "i mean one moment i'm twelve, the next i'm twenty six and one moment paps is five, the next he's nineteen..."

Gaster nodded, "IT'S SO WEIRD, WE REALLY NEED TO CATCH UP. I WANT TO HEAR ALL ABOUT YOUR LIVES."

"LET'S GO HOME. SANS," Papyrus looked at his brother, "WILL YOU?"

Sans smiled and looked to Frisk, "ready, kiddo?"

Frisk nodded, they were feeling a little awkward just standing and watching the reunited family.

They took a shortcut home.

Once back at the skelebros house they gave Gaster a quick tour and let him borrow some of Papyrus's clothes to change into. Then they let him sit down and rest while Papyrus cooked them something to eat.

Gaster had little time to rest, however, as the Dreemurrs were calling as were Grillby's family. The Followers were as well, even the ones that had fallen with Gaster were back. Everyone remembered Gaster and had questions. Gaster did his best to answer them and apologise for his mistakes. He was exhausted but he didn't want to sleep; he wanted to see his friends again, after all it had been so long since they'd seen him and Gaster was too excited.

It wasn't long before Asgore came rushing to the skeletons' house, banging on the door. Papyrus answered it and with a cheerful smile he lead Asgore to the living room. Before anyone could say anything or stop him Asgore rushed forward and pulled Gaster up and into a big hug. The old scientist let out a yelp of surprise before he laughed and hugged his friend back.

"I'm so sorry!" Asgore blurted out as he let go his old friend.

Gaster looked up at him, confused. "WHAT DO YOU MEAN YOU'RE SORRY? I'M THE ONE THAT'S SORRY. I DID SOMETHING STUPID, I PUT THE LIVES OF MY FOLLOWERS AND MY OWN SONS AT RISK. I... I COULD'VE TORN THIS UNIVERSE APART!"

Asgore shook his head and once again he hugged Gaster tightly. "No, it's all my fault. I wanted to free monsters by killing humans. I should've listened to Toriel. I should've tried to help you find another way. Instead I pushed you to act rashly. If I wasn't killing you wouldn't have felt so pressured. You could've taken more time, you could've found something else. You got erased because of me! Your sons became orphans because of me! I am so, so sorry, Gaster! I'm such a fool!"

Gaster sighed and shook his head and hugged Asgore back. "LET'S JUST SAY WE WERE BOTH STUPID. I'M BACK NOW AND I'LL NEVER DO ANYTHING EVEN REMOTELY LIKE THAT EVER AGAIN."

Asgore nodded and eventually he let go of his friend.

Papyrus then jumped into action, "I'LL GO MAKE TEA! WE HAVE SO MUCH TO TALK ABOUT!"

"sounds good, bro," Sans muttered. He'd been looking down at his phone the whole time and he didn't bother looking up.

"SANS GET OFF OF YOUR PHONE! DAD'S BACK! YOU SHOULDN'T BE TEXTING!"

Sans shrugged, "it's grillbz, he's asking me a lot of questions about what happened and how he and others have suddenly gotten their memories back. he said that as soon as he can find someone to cover for him, he's coming here. looks like asgore's not the only one who's just showing up to talk to dad... oh, tori's just sent a text, she's coming as well."

Papyrus sighed and bounced off back to the kitchen. "WELL IN THAT CASE WE NEED TO MAKE LOTS OF TEA! FRISK, WANT TO HELP?"

Frisk happily agreed and ran after Papyrus to help.

It wasn't long before Grillby and Toriel arrived. They also hugged Gaster and told him how happy they were to see him again. Before long more and more people began to show up at the Gaster household. It ended up as a spontaneous Welcome Home party. It ended up lasting quite a while and Papyrus and Frisk had to make a fast run to the supermarket for party food.

Even though it was all so sudden, Gaster didn't seem to mind. The party really confirmed to him that he was home, he was really back! He found himself enjoying it, it was so long since he had felt so happy and not just because he'd been trapped in the Void. He'd been depressed for a long time before the accident. He still felt hugely guiltily for what he put his sons through but seeing them happy made him happy. His sons had grown into fine young men, even if Sans was lazier than ever. They were happy, they had friends and a big house. They were on the surface, there was peace.

It was all so perfect but Gaster knew it wouldn't be easy to adjust to such a perfect life when all his life he'd been unhappy; war, trapped, constant fear someone or something would hurt his kids... He make a metal note that he should seek help. He didn't want to put his sons through anymore pain. This time he was going to think of them first, he was going to give them what they really needed not what he thought was for the best. He wanted to be better.

Things calmed down the next day and Gaster got to spend time with his sons and they spent the next few days catching up. It took a while but soon everything was becoming somewhat normal again. It soon felt as if Gaster had never left. Gaster loved his sons so much and it didn't take him long to begin doting on them again. He really did enjoy spending time with them and felt so horrible that he'd missed so much. He tired not to let it bother him but it did, especially with Papyrus, the little five year old was now nineteen and Gaster felt horrible about it no matter how much Papyrus said it was okay and that they could just make up for lost time now. That was what Gaster did, he spent as much time with both of his sons as he could. He soon settled into his new life.

He tried to retire but quickly got bored, after all his children were grown up and had jobs of their own. He went back to work as a scientist, working with human scientists and convicting Sans to come work with them as well. They rebuild The Core on the surface and continued research to improve it. A lot of Gaster's soul research helped a lot of people and he kept trying to learn more, not to end human life but to try to save it by curing and healing.

He also began to research the multiverse. It didn't take him long to built a new, safe machine in order to travel to other worlds. He and Sans made sure to go to all the nice universes with good Gasters to tell them how they did it so they to could get their Gasters back.

Sometimes Gaster had nightmares of what he'd seen in the Void but he never remembered it once he woke. He'd sometimes have a panic attack if left in the dark or in a small space. He had issues but he had his boys and his many friends, old and new to help him. He was also seeing a therapist as well which he found to be really helpful. Despite all the nightmares and fears, Gaster was so happy with his life.

He loved his job, he loved his family, he loved his friends and now he was there for them. He was back in their lives. After all the suffering and pain, Gaster was finally happy and he swore to never leave again. He never forgot those he lost; he would always miss his parents, siblings, in-laws and niblings but he had his sons. Two precious little miracles. He had a lot of regrets but making his sons wasn't one of them. They were the best things he'd ever made, they gave him a reason to life, they lit up his life and he'd love them no matter what. He was living on the surface, he was with his children, he was happy.

Doctor Wingdings Gaster finally had his happy ending.

AN: So this is the longest fanfic I've ever written. I'm honestly surprised with how much I managed to write haha. It's also the first fanfic I've written that didn't have any ships or smut/implied smut because when I started this I didn't ship any Undertale characters. I honestly found Undertale ships weird because not human... Yeah, now I ship Sansby, Papyton, and cute non-smutty Kingdings...

I'm really proud of how this turned out. I know it's nothing great and probably full of spelling/grammar mistakes (damn dyslexia) but for once I wasn't cringing at my own writing. Anyways hope you enjoyed it!

I'll probably write more Undertale fanfics but it'll most likely be ships...