Quickly but quietly, he padded through the kitchen, senses straining. How the hell had the intruder got in? He'd used everything he knew about home security to make his apartment as safe as possible. Where were they? The sound was coming from the bedroom. Cautiously, he peered around the edge of the kitchen door. Something wasn't quite right.

Suddenly, he realised what it was. Out of the corner of his eye, he could see a bottle of vodka standing out on the kitchen counter. He didn't drink it himself, didn't usually keep it in the apartment, though he'd been meaning to buy some more for Sienna's next visit. It would be an odd intruder who brought vodka with them.

Odd, or welcome. Very quietly, just in case he was wrong, he padded out of the kitchen and towards his bedroom. The door was open a crack, and through it he could see a familiar and reassuring sight. A battered blue suitcase. He knew now who the intruder was, and with it the answer to the riddle of how she'd got in. He hadn't asked Sienna for her key back the last time she'd stayed with him.

There it was again, he thought irritably, memory triggered by the recollection. The last time Sienna had stayed with him… there had been something he'd noticed, something he couldn't quite put his finger on, but which had caused his detective instincts to wake up and say, "Hey, there's something here you need to look at more thoroughly… something's not quite right." Maybe it had been something he'd not noticed? Something he should have seen, but hadn't? It was maddeningly unclear, and he shook his head with frustration. It would come to him eventually, if he stopped trying to force it.

Sienna was in his apartment… A smile crept over his face. It occurred to him to wonder why she wasn't staying with Juliet, or why she hadn't rung him. Well, she knew he was working undercover; that might answer one question, and as for Juliet, well, plans changed. Perhaps she'd just missed him. Or equally, perhaps she'd been feeling tired. His home was nearer the airport than Juliet's, and in a nicer area. He shivered slightly. He was still wet from the rain outside, and the apartment's heating was being sluggish in coming on. She might be asleep, he thought, as he very gently pushed open the bedroom door to avoid disturbing her if she was.

What he saw transfixed him. She wasn't asleep. Very definitely not. She was lying naked on his bed, eyes shut, head turned slightly away from him, warm curvy body framed by the dark bedcover underneath her. She was lying on top of the old t-shirt he occasionally slept in; he could detect his own scent in the air, her body warming it, mixing with her scent. He could feel his body responding to it, wanting her. For just a minute, the realisation that had been circling his head for a while whenever he thought of her, maddeningly refusing to come into focus, swam back up again. Perhaps if he'd been able to focus on it for a few minutes it would have come to him, but that was impossible with Sienna lying naked there before him. Suddenly, something – maybe instinct – had evidently alerted Sienna to his presence. Her eyes snapped open and she looked up. For a second, she looked startled, then her mouth curved up in a wide, wicked smile of welcome, and she held out her arms.

He needed no second invitation, instinct taking over completely as he literally threw himself on top of her. He heard her grunt slightly, but there was nothing unwilling at all in the way her arms wound around his neck and pulled his mouth roughly onto hers, thrusting her tongue in deeply. The shock of her warm body under his chilled flesh was enough to drive all other thoughts out of his head…

Some time later, he was vaguely aware of Sienna gently nudging at him, hinting that she'd appreciate it if he removed his weight from on top of her. He wriggled off her carefully, then reached across to pull the covers over them, rolling onto his side. She murmured "You're cold," in a tone of endearing concern, and snuggled herself behind him, spooning up with one of her arms under his head and the other gently stroking his chest and belly, her lips kissing his neck and ears. He finished wrapping the covers round them, and relaxed against her, savouring the warmth of her body against his back, her hands stroking him affectionately.

"Better?"

"Mmm... yes." He was beginning to see why she liked having him wrapped around her so much. Normally he liked to be the one doing the holding, liked seeing her curled up in his embrace - she'd once told him it made her feel safe and protected - but why not enjoy what she was offering? His back was really too broad and his body too long for her to wrap around him in the same way he could her, but the feeling of her warm, soft body against him was lovely. They stayed like that for a while, then he very gently rolled over, taking her in his arms and looking deep into those familiar green eyes, both of them smiling, Sienna's eyes half-closing with pleasure. It was a little unusual to be doing the kissing and stroking after the sex, but why not? She smiled more widely, chuckling very softly, and asked in a tone of lazy amusement, "So, nice to see you again. How was your day?"

"It just got a lot better."

"Me too."

She looked very, very satisfied. Now that he was no longer distracted by his hormones, he noticed a slightly sweet smell in the air, something on her. He glanced across at the bedside table and saw a glass of what looked like water, but which he guessed was probably vanilla vodka, Sienna's favourite drink if she was feeling down. He decided to take advantage of her mood and risked pushing his luck.

"You mind if I smoke?" Usually he'd not risk asking. She'd made it politely but firmly clear that whilst his habits were his own business, she didn't like the smell and particularly not on her. He tried not to smoke around her, and one of these days he'd quit altogether. But right now he really craved a cigarette.

She smiled and wriggled up into a sitting position, reaching for the glass. "Hell no. Let's be substance users together." He was aware of her watching as he padded naked across the room to find an ashtray, opening the window a crack en route. She leaned over and switched the light on. Autumn had come in fast, and the evenings were darker and colder. He was vaguely aware that she'd notice he'd put on weight, but one look at her smug, this-man-is-mine expression reassured him she either hadn't noticed or didn't care. He slid back under the covers, putting the ashtray on the table beside him and wrapping his free arm around her shoulders. She leaned her head against his shoulder, her breathing tickling his chest.

"So good to see you again." she murmured.

"You too, beautiful Sienna." He smiled to see her flush, and look down shyly. She offered him the glass; he shook his head. "Too sweet for me."

"Uh-huh. Bought it at Heathrow airport. Just as well. I had the worst flight ever over here; we had to stop at this little airport in the middle of nowhere when we got to this side of the Atlantic. I have no idea where it is, but it was surrounded by mountains, I guess there must have been thermals rising off them. Bumpiest landing I've ever had. I swear you could hear the wings rattle for every foot we went down. People praying, you name it."

"Sorry to hear that." He glanced across. She was looking thoughtful. "What's on your mind?" He should probably work round to asking her why she was here and not staying over with Juliet. The answer might be as simple as I missed you, but in case it wasn't, he decided not to push it just yet, to let the moment last a little longer.

"Oh, it's silly."

He gave her his best you-can-tell-me look. She gave him her best I-know-that's-the-look-that-fooled-a-thousand-suspects-don't-you-try-it-on-ME look in reply, then shrugged, and giggled. "Well before you came in, I was just wondering if secretly I'm a female chauvinist pig."

"Hmm?"

"I'm a modern, enlightened woman, but I fantasise about having this big, powerful, dark-haired, handsome guy pin me to the bed and take me roughly. Shouldn't I be trying to take the lead more?" Her tone was more thoughtful than worried, he noticed. She had come a long way from the shy woman in army fatigues who'd had to pluck up all her courage to get him into bed. "Shouldn't we be attracted to people for their personality? I mean, what about skinny, red-haired, nervous guys? If all women thought the same as me, they'd never get laid." She added hastily, "Not that I don't find your personality equally appealing. Odd, but appealing."

"Hmm…" He pretended to give that some thought. "Well, you know I only do that because you love it and it's what you want, you're in control the whole time, why not do what you enjoy? On the one hand, you have a point and society judges far too much by looks."

"And on the other?"

"For you, it's all academic. No guys, skinny, red-haired or otherwise, are going to get near you as long as I'm around, so fantasise away." He smiled evilly, enjoying her deep chuckles in reply. She took another sip of her drink, and smiled at him, looking him in the eyes.

"You know, for an enlightened man, you do sometimes manage to give the impression you'd like to chain me to the bedpost." Oh, there was an image. He thought about that for a while, and got a gentle elbow in the ribs. "You're smiling. You're ENJOYING that thought, aren't you?"

"It's a nice picture... Little collar, pair of heels, sulky expression."

"Leather bikini."

"I'm sorry?"

"If, hypothetically speaking, I happened to be someone's bedroom slave, I think a leather bikini of some sort would be called for, and probably a few bangles."

"You want to go shopping tomorrow?"

"I'm sure you can persuade me."

He leaned across to flick the ash off into the ashtray, and winced. She saw it. "What's wrong?"

"Ah, just a knot in my shoulder. It'll go away." She wriggled up behind him. One small hand made its way up his back and began to rub. Her hands were small but strong. Oh, this felt good. They stayed like that for a minute, then she pointed out, "This would be a lot easier if you were lying down."

"That makes a change."

"I'm sorry?"

He grinned, the mischievous grin that never failed to put an answering smile on her face. "Usually you like me on my back."

"Even you don't recover that quickly."

He stretched out on the bedcovers, noticing that the heating was finally kicking in, the room warming up pleasantly. Beside him, Sienna set her glass down and began to root through the bedside table's drawer. "The oil's at the back," he added helpfully. She found it and turned to settle herself across his back, but the bottle must have been slippery; it fell out of her hands onto the bed. With a muttered curse, she began mopping at the spill with some tissues.

"Don't worry too much, we'll have to change this sheet anyway," he pointed out, and was amused to see her blush… at which point, the maddeningly unclear thought about her that had been bugging him finally emerged out of his subconscious and smacked him between the eyes.

Sienna said she was on the Pill.

He'd never seen her taking it.

Worse than that, he realised with dawning horror, as the thought emerged with horrible clarity. The whole time he'd known her… she'd never had any periods.