'Rule 11,' the Doctor breathes in River's ear. 'There's always a convenient shrubbery.'
'There's nothing at all convenient about shrubberies,' River mutters. 'Especially not this one. For some stupid reason we're standing right in the middle of it and there are prickles and twigs and I don't like it.'
The Doctor slides a hand between her legs and presses his fingers just so. 'Sure about that?'
'I like your hand. I still don't like the shrubbery.'
There's a sort of silence, broken only by their breathing and the Doctor fumbling with her clothing. Then he pauses. 'River, are you wearing knickers?'
River stares at him. 'What do you mean "oh"?'
'Just that I'm further back in your time line than I realized. But don't worry, we can manage. Sometimes it's just quicker if —'
'Quicker isn't necessarily a good thing, sweetie.'
'It is if you're hiding in an old munitions factory from a Dalek patrol.'
River's eyes sparkle. 'Ooh, Doctor! Is that a spoiler?'
'Are you wearing pants?'
'Of course not. You were very insistent about that.'
'Ah. I mean, you will be.'
River unzips his trousers and slips a hand inside. He makes the most interesting noise in the back of his throat.
'Ooh, future me is lovely and persuasive, isn't she?' River purrs in his ear.
'Oh yes. And very inventive.'
'I can be inventive, too.' River isn't going to be outdone by anyone, and that includes her future self. 'Lie down.'
The Doctor blinks. 'What, here?'
'You're the one with the tweed jacket who has rules about the convenience of shrubberies, so you're the one who gets to lie on a bed of thorns...'
'Rule 11 is rubbish. I'm rewriting it.'
'... and I'm the one who gets to ride you like my favourite pony.'
'Oh!' The Doctor descends to ground level with pleasing speed, accompanied by the hideous sound of snapping twigs.
River starts to see the Doctor's point about knickers when she tries to wriggle out of them. It's not very easy in a shrubbery, but at least his ardour doesn't seem in any way diminished. Not even when his bare behind is squashed against prickles and twigs as she finally sinks down onto him.
After that, there's a lot of thoroughly satisfactory jiggling and bouncing (her), writhing and thrashing (him) and panting and moaning (the pair of them). When it's all over, River leans forward, settling onto the Doctor's chest with a sigh of contentment. He gives her a giddy sort of grin.
'I have a twig up my bottom.'
She stares at him, nonplussed. 'Well, it took you long enough to complain!'
'Oh, River, that wasn't a complaint. Just a helpful observation.'
'Then I need to file it away for future reference.'
'Yes, you do.' If the Doctor ever looks any smugger, River thinks the universe will gasp in disbelief and then set about redefining the word in his image.
'So what happened to spoilers?'
'Sometimes they're vastly overrated.'
River edges the tip of one finger along his collar-bone. 'We're in the gardens of the Most High Potentate of Jasthrenilania where shrubberies are not exactly hard to come by, but I'm sure the same isn't true of old munitions factories surrounded by Daleks.'
'They have what I like to call shrubbery substitutes. Rusting machines and other handy factory ... things.'
'So basically anywhere we can safely have sex is a shrubbery substitute?'
'I wouldn't go so far as to say safely, what with dangerous places and Daleks and so on, but ...yes.'
'And we do that sort of thing a lot, do we? Have sex in dangerous places surrounded by our enemies?'
'What do you think?'
'I think Rule 11 is going to be my new best friend.'
The Doctor skims one hand over her tangled curls and smiles. 'Yes, it is.'