Kate was in the middle of storing her groceries in the fridge, when her door bell rang. Shit, who could that be? With Castle having to work on his book, she was looking forward to a quiet evening with a hot bath and a glass of wine. Visitors were definitely not welcome right now.

Irritated, she flung her door open and came face to face with Detective Inspector Colin Hunt of the Scotland Yard.

"Surprise," he smiled, as he greeted her.

"Hey," she returned and her anger regarding the unannounced visitor quickly dissipated. "Since when are you in town?"

"This morning," Colin replied and wrapped his arms around Kate. "Some complicated case I'm liaising with Interpol. Don't ask. I came as quickly as I could get out of the meeting."

He pressed her close and let his lips travel across her face in kisses. Kate draped her arms around his neck and pulled him even tighter. Finally his mouth found hers and she opened her lips to grant his tongue access. They kissed passionately until they had to gasp for air.

"Hmm, missed you," Colin hummed into her ear. Kate laughed out loud. She could clearly feel how happy he was to see her, since it was hard to ignore his erection. And if the tingling between her legs were any indication, she was really happy to see him, too.

"Come inside," Kate said and dragged him into her apartment, realizing they were still standing on the threshold of her door.

While Kate closed the door, Colin took off his Jacket and shoes. He wanted to pull Kate in for another kiss, but she stopped him with her hand against his chest.

"There's been some developments since the last time," she answered the question he hadn't voiced out loud, "Castle and I are together, now."

"So?" He looked at her confused.

"I just thought you should know that," she explained and lowered her gaze with guilt.

"Kate," Colin said and lifted her chin with two fingers, so he could look into her eyes. "I've always known that you belong with Castle. There's never been any doubt about that, so it's okay with me. I like hooking up with you, when I'm in New York, but I also know that that's all we'll ever be." He gave her a calculating look. "The question simply is do you want me to leave and be out of your life forever?"

Kate pondered her decision carefully. She loved Castle more than anything, and she had very strong qualms about cheating on him, but she just couldn't miss out on one of her rare hook ups with Colin. There was something about the Brit that made him irresistible. Whether it was his accent or his well-toned body, Kate didn't know. What she did know was that she couldn't let go of him.

"Stay," she made her decision and the word had barely left her mouth when Colin crowded her into the next wall. He plunged his tongue into her mouth and squeezed his hand into her pants. His fingertips parted her wet lips and Kate moaned into his mouth.

God, yes, she wanted him.

Her hands slipped underneath his sweater and he interrupted their kiss only so long it took her to pull the garment over his head. Kate unbuttoned his pants blindly, dragging the zipper down, so she could bury her hands in his underwear. His hot and hard cock pressed into her palm.

They kept stimulating each other like that, and Kate was just about to suggest taking things into her bedroom, lest she came in her clothes, when something caught her attention out of the corner of her eye. She turned her head and saw him.

Castle.

He gazed at her stunned and Kate stared back at him in shock. Colin came to his senses first and pulled his hand out of Kate's pants.

"Hi Castle, how's it going?" He tried for nonchalance.

Speechless, Castle placed the wine and bag of Chinese onto the kitchen counter and turned to leave. Coming out of her shock, Kate sprinted after him and grabbed his arm.

"Rick, please, let me explain," she implored him.

Castle turned around slowly, but instead of the anger she expected all she could see was disappointment. She didn't know what was worse.

"I can't wait to hear your explanation for this," Castle shook off her hand and fell unto the couch. He prompted her with his eyes. Kate straightened out her attire and ran her fingers through her hair. She was stalling.

"Colin's here on business." Kate started.

"Oh!" Castle sneered, "Well then that explains everything."

"Rick, just please," she begged him again and Castle held up his hands as an apology. "Remember the case we worked with Colin?" He nodded. "I slept with Colin after we closed it."

"Still doesn't explain why I caught him with his hands down your pants now." Castle fretted.

'Yeah well, we've been seeing each other when he's in town ever since." Kate clarified.

"You've slept with him, while we've been together?" He asked her with disbelief.

"No, of course not!" Kate shot back. "The last time I saw him was half a year ago. We weren't even together then."

"Kate, clearly things aren't as black and white as you make them out to be," Castle noticed. "If I hadn't walked in on you, the two of you would be lying together in your bed, right?"

Kate looked to Colin for help, but he just shrugged his shoulder, sporting a grin.

"Okay, Castle, you're right." Kate rubbed her eyebrows and sighed, "And I'm sorry. It won't happen again."

"Ha!" Castle jumped off the couch. "I don't think so. I saw you. You were a goner. Do you want to leave me for that limey?" He yelled and threatened Colin with a finger.

"I better leave," Colin reasoned and pulled on his sweater.

"No!" Kate yelled back and both men looked at her surprised. "I mean, no, I don't want to leave you, I love you", she spoke to Castle with a quiet voice. "Only you," she added with more confidence.

After a moment of silence Kate walked over to Rick and took his hand, then reached with her other hand for Colin, who took it hesitantly.

She looked between both men and sighed deeply. "Why can't I have both of you?" She asked quietly.

"You're not being serious, Kate, are you?" Castle shook his head in disbelief and freed himself to pace the floor.

But Kate simply nodded, "I am."

"I'm game," Colin interjected, earning a glare from both Kate and Castle.

"Could you give me a minute alone with Castle?" It was really more of an order than a request. Colin nodded and moseyed into the kitchen, where he stuck his head into her fridge in search of a drink.

Kate followed him with her eyes and once she was sure he was out of earshot, she turned back to Castle. She walked over to him, clasped his hands in hers and gave them a squeeze.

"Rick, I love you," she whispered lovingly, "and I wanted to spend the rest of my life together with you."

"But?" Castle studied her eyes carefully.

"There's something about Colin I can't resist. I can't even tell you what it is about him, but I want him." Kate sighed, "I'm so sorry."

"And to keep me from pouting you want to include me in your little sex games?" He asked her skeptically.

Kate laughed, "Do you remember our ski trip?" Caslte nodded. "That night we spent together with the ski instructor?" Now Castle was grinning. "That was one of the hottest nights I've ever experienced. That was your fantasy having two women together. And we lived it out. I've got threesome fantasies, too, only it's with two men and one of them should definitely be you." She looked at him questioningly. "Now it's my turn. Do you think that's something you could live with?"

Castle stepped into Kate's personal space and rested his hands on her hips thoughtfully. She could see the cogwheels in his brain turning. After what felt like eternity a grin spread over his face.

"The more I think about it, the more it turns me on just thinking about watching another man satisfy you." Castle wrapped his arm around her waist and pulled her flush against his body. "And Colin's a pretty nice bloke after all."

Now it was Kate who was surprised at how quickly Castle took to her idea. "Are you sure?"

"No," he replied on a smile, "but I love you. And if that's what you want, let's do it." He pointed to Colin who was leaning against the kitchen counter, nursing a bottle of beer. "But first I want to talk to him. Alone."