Oliver's last words are an order.

"Run, Barry. Run!"

Then he bursts into flames, killed instantly.

Barry's so scared he doesn't know where he finds the strength, except maybe the fear is his strength, because he's running as fast as he can, flying down the streets, feeling the wave of heat behind him and knowing with absolute certainty that unless he runs faster he's going to die. There won't be anything left to salvage or anyone left to salvage him; just a scar on the Earth where their home once was.

His existence will be wiped clean from history, as will everyone else he knows and loves.

So he runs furiously, frantically, pushing himself as hard as he can. His heart feels like it's going to beat out of his chest but he's almost immune to his own physicality: he's faster than sound, faster than death, and he's only going to survive if he pushes himself harder.

He has to make it count. He only gets one shot at this.

Feeling a new sort of terror take hold as the heat closes in, he hears Oliver shout, Run, Barry. Run!

Knowing everything at stake, he finds it in him to push faster, harder, and break the barrier of light, of time, and even though he knows it's coming it's still bizarre, off-putting, when he sees his younger self Flash by, jogging, absolutely no urgency to his step.

You're running into a death trap, he thinks, and then he yells as something fundamental snaps and his younger self vanishes and he comes to a halt in an abandoned warehouse.

"Thank you for coming," Oliver says calmly, standing tall and proud and unscathed, and Barry wants to collapse for how powerful his relief is. "I know this is more than a little crazy."

You're telling me.

He's dizzy and trying not to breathe too hard, trying not to think about the fact that he's just destroyed his younger self, that he is his younger self, that the Flash running from the heat wave doesn't exist anymore.

You get one shot, he thinks, staring at Oliver and trying not to because he's going to draw attention to himself and he can't let any of them know or he'll get them all killed.

So he keeps his mouth shut and somehow manages to keep from sinking to his knees, exhaustion sweeping over him, heart still pounding as he stares at Savage and thinks, You're the man who murdered them. It's hard to look at him and not see Oliver faltering, Kendra gasping, the world going up in flames. He has to focus, but he can't, not when he has less than twenty four hours to stop it from happening.

"Bring Khufu and Chay-Ara to Jurgens Industrial in twenty four hours," Savage says, utterly calm, his face a blank mask of rage, "or I will see you dead and buried under the bodies of your loved ones."

He turns and walks away and all Barry can hear is shouting, feel a wave of heat as Oliver gasps, "The gauntlets aren't working! You got to let go, Barry!"

He can't breathe – he's going to start hyperventilating if he isn't careful – and he's trying to remember how to inhale, exhale, inhale, exhale–

"Barry, you all right?" Oliver asks, looking confused and concerned.

Barry tries to nod, can't put up a smile, and settles for a scarcely audible, "Yeah." Clearing his throat, he finds his voice. "Let's go."

Oliver nods, leading the way, and Barry falls into step easily behind him, trying to remember how to put one foot in front of the other. Everything feels intensely more real – he picks up every nuance, the tiny crunching sounds of dirt underneath their feet, the rustle of a bird taking flight, crickets, the distant chatter of city traffic, the way Oliver moves, the way the world smells, grassy and earthy and home.

You only get one shot.

He watches Oliver rev his motorcycle and take off, peeling off into the darkness, and Barry has to swallow the irrational urge to yell at him.

It's a trap, it's a trap, everyone's going to die—

Instead he plants his feet, draws in a deep, comforting breath, and takes off.

His muscles shake under the suit when he comes to a halt outside of their safe house, doubling over and breathing hard. Oliver's already on the move, talking and walking, making plans that won't work, and Barry wants to yank his hair out because what's the use in going back in time when he doesn't know how to fix it.

When Oliver reiterates the need to brief the team and make a plan verbatim, Barry loses it.

"It's not going to work."

Oliver pauses, gravel crunching underfoot. "What?"

Fuck.

"Mm, nothing. All right, never mind. I shouldn't have said anything."

Time is an extremely fragile concept. Any deviation, no matter how small, could result in a cataclysm.

"What's going on?" Oliver asks.

He can't help it – he told Cisco, who didn't want to know but someone had to know what was coming, he couldn't be the only one responsible for the future.

No matter how much better it would be for all of them to live in truly blissful ignorance, to set aside the destroyed timeline and run as far from Savage as they can, Barry knows it isn't their destiny, either.

Which means he has to break. He has to try.

To hell with continuity.

"Okay, look, this isn't going to make any sense to you," he says, and he's fevered, frantic, desperate to convey his point. If Oliver benches him now, they're all going to die. "But I – all right, so I traveled back in time from when we tried to take out Savage – I mean, later. When we try to take him down – in the future. And it doesn't work."

He tries to picture himself from the outside. My name is Barry Allen. I'm from the future. And I'm here to stop it from happening or you're all going to die.

It's crazy. It's worse when he flips their positions, trying to imagine a rogue Oliver appearing to tell him that the logical, the reasonable, isn't going to work and they're all going to die if they don't come up with – something different.

Oliver doesn't have any powers, doesn't have the benefit of seeing the impossible unfold in front of him every day, and his world is still, for the most part, stable, sound, sensible.

So his response is charitable: "You're right, that . . . doesn't make any sense to me." His face is flat, hard to read and Barry wants to just shake him and say, I watched you die, you have to believe me, we have to fix this.

Feeling frustrated and scared, Barry shrugs and concedes, "My world is stranger than yours."

Oliver's face is soft, almost sympathetic, and when his expression resolves into determination, his voice is calm, clear. "Well, maybe we can use that to our advantage. You say that whatever we do against Savage doesn't work? Then we come up with a new plan."

Any deviation, no matter how small, could result in a cataclysm.

"No," Barry says, not sure why he's trying to stand still when time is pressing forward, pushing him inexorably towards the brink, "no, no, no. Okay, look – you can't, you—"

"Mom," he sobs, trying hard not to rush her to the hospital, to save her – she can't be saved, she's beyond saving, but he still feels the urge rise up powerfully in him, knowing that he can't, he can't, he can't, but he wants to, he still wants to, and he's a coward, he's afraid to change it all, he can't change it all, he loves who his family is, he loves them, he loves them, he loves them, he can't do this to them, but he's killing her, too, as surely as the Reverse-Flash is, letting her die when he could save her, and his heart is splintering into a thousand painful pieces as he clings to her and sobs.

"Mom."

Eyes clouded with pain, he shakes his head and says, "You – when I mess with time, it just – it doesn't end well."

I killed Mom.

The Reverse-Flash killed her.

I let her die.

Oliver's voice is grounding, real, pulling him away from that dark room, that hurricane of pain. "But what you're telling me," he says, voice steady with utter conviction, his eyes bright as he begins to understand, "is that it already doesn't end well. Barry, people in our line of work, we don't get second chances," he says, and he's grinning, he's joyful, and Barry doesn't get it, he should be trying to commit Barry, but instead he's actually listening and how, how can he believe things are going to end well when Barry knows what happens?

"We need to take this one," Oliver finishes, bright, certain, and Barry's trying not to let himself fall into the trap, the optimism, but he trusts Oliver, he has to, and this is why he came back, isn't it? To fix it.

Which means he has to take the chance that they're going to break it instead.

If I fail, nothing changed.

"All right," Barry says, and it hurts, because he knows how badly this can end, he knows what will happen to Oliver – what will happen to everyone – if he fails. Out loud, all he says is, "I hope you're right."

Oliver nods, and it's that simple, unspoken of course I am that sets Barry's world on its axis again.

"All right," Oliver echoes, leading the way towards the safe house, "let's start with what went wrong."

. o .

Barry's struck with déjà vu every time he looks around the room.

He can't stop imagining their shock in that breathtaking instant before death, feeling a new surge of guilt every time he thinks about how much they trusted him to keep them safe, how they left their lives in his hands and he let them die.

(You let her die.)

He can't stop hearing Oliver's choked command, his hands shaking hard, his body approaching disintegration from the sheer force of the scepter. You're fast enough to get away. Go!

He can't stop seeing the flames.

Every time Barry looks around the room, he's struck with a profound sense of loss, so crushing he can't breathe, he has to force himself – inhale, exhale, inhale, exhale—

But they're still alive, still breathing.

And he has to keep it that way.

He runs into burning buildings, runaway trains, straight to the heart of a crisis – just to save strangers.

These are his friends.

Failure isn't an option.

When Kendra says, "I think I know how to stop him," Barry swallows hard and wills his stomach not to turn over.

It's going to work this time.

Fetching the meteorite is almost a blessing; the blast of fresh air helps him clear his head long enough to offer something to the conversation.

He tries not to say much, to keep his head down, his voice low, let time be, unperturbed, but he already knows they've tampered with it irrevocably.

You only get one shot.

Oliver looks around the room and Barry does the same, and he knows they see two separate pictures, two different futures, and Barry thinks, Please be right.

"Where do you need us?" John asks.

Oliver looks at the room and Barry can feel the difference, almost as much as he hears it:

"Suit up."

And the time continuum rifts.

Barry hopes the faintest hint of smoke is his imagination and not an omen, but he still excuses himself long enough to sit on the floor in his room, hold his head in his hands, and shake.

He hears footsteps and pushes himself upright, using his speed to his advantage, regaining his composure and throwing his suit on in a fraction of a second.

"You ready?" Cisco asks, solemn, but determined.

Barry lets out a long, painful breath. "I hope so."

. o .

Barry's heart is beating so fast he's afraid he's going to pass out before they even meet Savage, but somehow he manages to hold himself together as they step inside the warehouse.

"Are you sure about this?" he asks Oliver, needing to hear it, needing something to replace the burning smell trying to overwhelm his senses. "About changing the future?"

Oliver looks at him and says, very seriously, "Barry, what can happen here that is worse than what already did?"

He has to stop himself from saying, There are other ways to die.

"If I knew that," is all he says, "I wouldn't be so worried."

Oliver doesn't lie to him – doesn't say it's going to be okay – but it's there in every line of his shoulders, tall and unfolding, ready to face down anything. "Let's do it."

. o .

It happens in slow motion.

He waits for Savage's step to falter as the multi-pronged assault slowly batters down his defenses, and then he's rushing forward into the fray, keeping an eye on everyone – you only get one shot – because he'll never forgive himself if any of them get hurt, if anyone dies, and then he's got the scepter in his hands and he's firing at Savage.

He can barely feel anything over the vibration and heat, and he's peripherally aware of the others flying to safety and buckles down hard, gritting his teeth and holding on for dear life.

Oliver rushes up to his side and all but cements him to the floor, his strength a ferocious counterpoint to the backlash from the scepter, and Barry feels safer and stronger and more powerful, but he can feel the timelines closing in, his whole world threatening to shatter apart as two destinies fight and all he can hear are Oliver's last words.

Run, Barry. Run!

"No, no, no, Oliver, get yourself to safety," he pleads, gasping, scarcely capable of dedicating strength for speech.

"We're not leaving each other!" Oliver shouts, throwing it in the face of the universe, daring it to defy him, and Barry can hear the echo, the promise—

If you need me, I'll be there.

Until the bitter end.

There's a moment when everything stills and over the roar of the fire Barry feels the tiniest shift in Oliver's shoulders, resolution written in every line, and then they're leaving back and shoving the scepter forward, a blast of heat erupting from the end.

Barry sees the flash of light and Savage's charred, disintegrated body in the instant between death and pulverization.

And he thinks, It's over.

The scepter vanishes, and there's noise and people and he really does need to keep track of it all, but all he's really aware of over the racing of his heart and the pounding in his head is Oliver's satisfied, almost swaggering walk as he turns to them and says, "Let's go home."

. o .

Watching Felicity and Oliver hug is almost as satisfying as beating Savage.

Watching Cisco try and pop a bottle of champagne before sighing deeply and holding the bottle out to Caitlin – she snaps it off easily – is almost as rewarding.

Watching them, and letting himself be a fly on the wall to their worlds, their crazy, wonderful lives, Barry accepts the champagne Thea hands him and offers a toast.

"To Starling City's finest," he says.

"To Central City's," Felicity rejoins.

"Cheers," Oliver says, clinking glasses, and there's laughter and drinks and hugs (somehow, Oliver avoids all of them, with one wonderful exception that has Felicity smiling all night, and Barry vows to fix that soon), pizza from the best joint in town ("this is harder than it looks," he says, balancing six pizzas precariously in his grasp; Oliver single-handedly polishes one off), and a ringing feeling of triumph, of closure, of family.

Everyone's home.

Everyone's alive.

And, at last, Barry feels, everything is exactly as it's meant to be.