It took a month for her to realise that it wasn't entirely innocent. Even then it was accidental, when some particularly angry turbulence dislodged the Doctor from the console and he landed on top of her flustered, blushing, and hard. Something dark and ancient in his eyes told her that this time it wasn't personal, and when he scrambled back to the controls she noticed for the first time how deliberately he brushed against the rows of dials and switches.
There was an element of performance to it, some exotic silent music lifting from his fingers as coaxed the ship back to stability. She knew those movements, the ways his hands found curves and his nails scratched just so when he flicked switches.
It was weird, but the Doctor was weird himself. For all Martha knew it was normal for his species. She'd caught him talking to the TARDIS more than once, had smiled at his eccentricity and filed it away under 'Adorable'. She moved it to 'Kink' when she realised what she'd somehow missed before.
Which was how she discovered that it wasn't a one-sided affair.
"It's very phallic," she'd said, because there wasn't really an innocent lead-in to what she had in mind.
The Doctor stopped flipping switches and stared at her across the console. "Pardon?"
She nodded at the oscillating rotor between them. "That. It's very phallic. The way it sort of... thrusts up and down."
He sighed at her. "Why is everything about sex with you lot?"
"You always say that. You always say that and then you shag me anyway. You just like pretending you're above all that. Do you think it makes you more impressive? It is a compensation thing?"
She saw him run his hand along the edge of the console as though soothing the machine inside. He saw her staring and stopped, met her gaze with one that dared her to say something. Things happened when he looked at her like that. Mostly good things, but it was always risky.
Sometimes Martha liked taking risks. She'd learned that from the Doctor.
"Is it a general machine fetish or do you only want to shag this one?"
"I don't mind," she said, moving round to meet him, "it's not like you're the only person ever to have a weird fetish. I've done shifts in A&E, I've seen objects stuck in places they're not supposed to go."
"Martha Jones, that's the least erotic thing you've ever said."
She grinned and touched his chest with a hand. "We could do it on the console."
He took a step back and stared at her as though scandalised.
"Oh, come on, it's not like you haven't thought about it."
"I've never thought about it," he said, flatly.
"Nice solid surface, very suggestive height..."
"Lots of buttons that shouldn't be pushed."
"Plenty of things to grab onto."
"And we're back to everything being about sex. Next you'll be asking me about my mother and whether I've ever had dreams about waterfalls."
She looked at him for a few seconds, then leaned back against the console. "I wouldn't touch anything dangerous."
The Doctor ran his tongue over the backs of his teeth and studied her carefully. "You might not like it. You might think it was too weird."
He took her hands and tugged her to stand up. "If it makes you uncomfortable, just tell me stop. Agreed?"
"You were in the Girl Guides?" He put a hand on her shoulder and spun her slowly to face the control panels.
"I don't have the uniform anymore, if that's what you're asking."
"I'm not. This alright?" He'd pushed her gently until she was bent over the console.
She let him place her hands in what were presumably safe spaces on the console. "It's not like this is the kinkiest thing I've ever done."
"Interspecies sex is considered a bit kinky by some people." He pulled down her jeans and her underwear, slipping them off with her shoes and dropping them by her feet.
She shivered under air and fingertips. "One of these days I'm going to gag you."
"I might hold you to that, Miss Jones. You have a lovely rear view. Have I ever told you that?"
"You might have mentioned it once or twice." She felt his fingers slip into her and her nails dug into the panel under her hands.
His fingers stilled inside her and his other hand touched her back. "Careful."
"You'll hurt her." The hand on her back traced her spine. "Is it getting too weird yet?"
"Can it really feel that?"
"Yes. No. Sort of. It's difficult to explain."
Martha stroked a hand along an unoccupied bit of console. "That?"
"Harder. So she can feel it."
She pressed down harder on her second attempt. "It's not weird," she said, "it's just a bit..."
He moved his hands to her hips. "We don't have to do this if you don't like it."
"I feel a bit... stupid."
He sounded disappointed, so she shook her head. "No, it's just... I feel a bit daft stroking a machine, that's all. I don't mind, it just seems a bit one-sided."
The Doctor knelt and picked up her discarded clothing. "Right, let's forget about this. Bad idea, no one's fault. In fact, let's never mention it again."
Martha didn't move. "You said it can feel things. Did you mean that or was it part of some fantasy thing?"
She heard fabric hitting the floor again. He took her left hand and moved it to the rotor in the centre. "Listen," he said, quietly.
The Doctor stroked his fingers along the console, a careful pressure. Martha felt rather than heard something sigh.
"She's sensitive," he whispered. "She feels this," he slid his hand down the panel, pressing his fingertips to a pure white, "because I want her to. I can let her feel things I feel, and she can do the same. It's... it's part of our connection. It means she can tell me when something needs fixed, it means we can always find each other."
Martha felt vibrations creep along her skin. "Is it... is this normal? The sex part of it?"
"Says the woman with no knickers on in an alien spaceship."
"You know what I mean."
"We're close," he says, as though that explained everything. He moved his hands back to her hips. "Are you sure you want to do this?"
"Might as well."
"How enthusiastic of you." He slipped a hand between her legs. "All you need to do is... think. Let her feel what you feel, let her know what you're doing. It's a bit intimate, I'll understand if you don't-"
She pushed back against him. "If you don't get started soon I'm going to go and have a wank instead."
"I was only making sure. It's not like I do this every day." She heard his zip open, felt fabric and then skin against her. He moved her hands to the safe spots, placed one of his hands over one of hers. "All you have to do is feel," he said, and then slid smoothly into her. Martha felt air rush from her lungs and her palms tingled with something that wasn't quite electricity.
"She's old," he said, half-breathless. "She needs to feel to keep going."
Martha pushed back, trying to find the rhythm. "You love her," she said, knowing this suddenly and with the clarity of crystal.
"There's no life without love." He traced his fingers across the nape of Martha's neck and someone thought for her take this, keep this, it might be the closest he ever gets to saying it to you. She breathed against the alien surface and let something guide her fingers the right way.
The three of them moved, thought, breathed, and it was weird, but at the same time it was natural. At moments she felt like an intruder, but then a touch or a lick distracted her so very deliberately and she put worries aside for later. When she came the air was hot and humid and the machine purred with her, a melody for her thumping heart and gasped-out cries. The Doctor followed her with a strangulated yell and maybe she just imagined the sparks along her spine.
The Doctor whispered something to her that she didn't understand, kissed her shoulder and turned her to an embrace. "It's not normal," he said, without apology.
"Nothing is," she said. "Not for us."
She just wasn't sure which 'us' she meant.