exothermic: adj. (of a reaction or process) Accompanied by the release of heat.

"Castle -"

It's hours later and she's on her back in his bed, gasping as he laves his tongue over her stomach, his fingers trailing over her hipbones.

After giving statements at the precinct, they got a blessedly quick reprieve from Gates, who told them go home, you've had a long day.

They didn't argue; they hurried downstairs and caught a cab back to his place because it was entirely too many hours of not touching and she desperately needed to get him back into her skin.

And he knows, somehow. He's slow and methodical and patient, tugging her shirt over her head, sucking at every inch of skin he uncovers. It's slow and hot and torturous but honestly it's a better kind of waiting than what she did for most of today. Kate threads her fingers through his hair, her eyes fluttering shut, a long moan escaping her lips as she arches under his clever mouth.

The first time he takes her apart, his mouth and fingers between her legs, she cries out, her toes digging into his back, her hands fisted in his sinfully soft sheets. Her hips jerk uncontrollably and he pushes her back down into the mattress, working her deliberately until the last shivers of her orgasm run out and she's left panting and glowing.

He tugs her on top of him after that and she rides him with abandon, grinding her hips into his, her fingers buried in his hair. She sucks on his tongue and moans into his mouth and then he slides a hand over her spine and thrusts into her messily as she rocks into him and she comes hard, bowing into his touch as he spills into her, hot and perfect. Her body is burning and her head is spinning and it feels like their first time all over again, because I love you is still clinging to her like light, the unbearable bloom of alive mingling with the shiver of love that makes her lips tingle and her fingertips buzz and her skin glow from inside out and she thinks she's never, ever going to be cold again.

She curls up in the warmth she'd thought she was losing forever, tracing patterns on his chest absently while he runs his hand through her hair.

He takes in a long breath and she feels his chest rise under her cheek. "You love me?"

"Mmm." She stretches up to reach his face and kisses him slowly. "I do."

"You love me."

"I love you," she repeats softly, propping her head up on her hand. "Not taking it back now."

"I know." He's got that sleepy grin, the stress from the day taking its toll, and she knows he'll be out before long. "Just like hearing it."

She whispers it into his lips again. And again. And again.

Castle dozes off not long afterwards. His face is smoother in sleep, the tension melting away. His shoulders relax, his face calms. He looks younger.

She's still wound up, and it's early, so she kisses him softly on the lips, shrugs on his bathrobe, and pads out into the kitchen to get a glass of wine.

She's just heading back into his study when she hears her phone ringing from his desk; she'd left it plugged in there. Sipping her wine, she curls up in Castle's desk chair and checks the caller ID before answering. "Hi, Dad."

"Katie? Sweetheart? I got your message. Is something wrong?"

"Um." She wonders if there's a good way to recount her day. Probably not. "It - was kind of a bad day, Dad."

"Bad how?"

"Well. I - stepped on a bomb."

It takes her a long time to calm him down, and she wishes she'd just gone to his place to talk to him in person, because she knows he still worries about her every day. But she finally gets him to accept that she's okay.

"Really okay, Katie?"

She smiles. He knows her too well. "Shaken up, yeah. But I'm going to be fine, Dad."

"Good." His voice is a little shaky but he seems to have evened out. "You said Rick was there too?"

Just hearing the name Rick makes her breath catch in her throat, and before she can stop herself she's crying quietly, tears slipping down her cheeks.

"Katie?"

"Yeah. He was." She takes in a long breath through her nose. "He wouldn't leave, Dad. I kept telling him to go - the bomb squad told him - but he wouldn't leave."

"Oh, Katie - "

He saved my life, Dad -" the tears are streaming freely now and she doesn't bother trying to stop them - "just because he was too stubborn to admit it was over."

"Is he there right now? Can I talk to him?"

"I - well, he's asleep, but - hang on."

Not that she wants to wake him, but Dad wouldn't be asking if it weren't important.

She pads into the bedroom and settles beside Castle, rubbing his arm gently, leaning over to kiss his cheek. "Castle. Rick. Wake up, Castle."

"Mmmmmfff. Kate?" he mumbles, his voice thick with sleep. His eyes blink open. "Wha's wrong?"

"Nothing." She brushes her hand over his cheek gently. "My dad's on the phone. Wants to talk to you."

That seems to wake him up right up; Castle blinks, the confused, glazed look clearing up, and he sits up in bed, scrubbing a hand over his face. "What does he want?"

She shrugs, handing over the phone. "Not sure."

He purses his lips but takes the phone, clearing his throat. "Jim? Hi." Pause. "No, no trouble. What can I do for you?"

There's a long pause after that, and Castle's face goes very sober. He looks back at Kate, and she can read in his eyes - this is something between the two of them.

So she brushes a quick kiss to his lips and goes back out to the kitchen, stopping to grab her abandoned wineglass from his desk.

She's curled up on the couch, flipping idly through Heat Wave, when Castle finally reappears. He's tugged on boxers, and his hair is still mussed from sex and sleep.

He slumps wordlessly on the couch beside her, sets her phone on the end table, and silently crushes her to his chest in a powerful hug that knocks the breath from her lungs, an embrace that's more desperate than soft.

An embrace that says I was so scared, Kate.

She twines her arms around his neck, breathing him in slowly. His hugs are strong, encompassing, and she just loses herself like this, completely wrapped in him.

"You okay?" she murmurs.

"Your dad's a smart man."

"He likes you."

The one flaw in his otherwise perfect judgment."

She huffs a soft laugh and presses a gentle kiss to his throat. "Hardly."

They fall silent for a long time; Kate shuts her eyes, letting the steady beat of his pulse lull her towards sleep. The adrenaline and afterglow are worn off; she's tired now, her whole body weary.

"Castle," she whispers. "I don't think I could have done it without you."

"Yes you could." He tips her head towards his and kisses her gently. "But it wouldn't have been as much fun."

He scoops her up into his arms and carries her into the bedroom, where he sets her gently in bed and curls up beside her, his arm slung heavy and warm over her waist. She's still wrapped in his robe; it's soft and fluffy and smells like him.

She falls asleep hearing him whisper I love you too.