I've used dialogue from the show at the start of the scene with Tom and Mary.

It wasn't until she was bathing the morning after their desperate, frantic coupling that Mary realised they hadn't used any protection. The thought crossed her mind that if Tom had got her pregnant, he'd have to get off his high horse and do the right thing. Part of her thought perhaps a baby wouldn't be too high a price to pay for that.

But as Mary had tossed and turned in her bed analysing everything he'd said, one thought had planted itself in her head and it had given her an idea.

However unfathomable his reasons, Tom's plan seemed to be to simply rewind the clock and ignore everything that had happened between them. But his plan had a fatal flaw, namely that he was as deeply attracted to her as she was to him. If nothing else, last night had proved that. And that gave her power over him.

All she had to do was wait out this mini crisis he was going through and then seduce him. And she was willing to seduce him as many times as it took. But she'd have to be clever about it, play the long game.

And, she reasoned, history was on her side. Throughout her whole life, what Mary Crawley wanted, Mary Crawley got. And Mary Crawley wanted Tom Branson more than she'd ever wanted anything or anyone ever before – including, she realised with a sickening jolt, Matthew.

She bided her time, summoning every bit of her social skills to live and work alongside him, without once referencing their affair or betraying her intentions. She watched Tom go from wary and skittish around her to something approaching relaxed and relieved, apparently believing she was taking him at his word. To be fair, during these weeks, their relationship regained some of their old, easy camaraderie, similar to how it had been before they fell into bed together. Mary had missed that and was happy it was back, but it didn't deter her from her mission.

Opportunity knocked in the form of Evelyn Napier inviting her to dinner in London. Henry Talbot would be there, and Mary, to her slight shame, was not above using his interest in her to further her pursuit of Tom if necessary. When Tom wished her well for her London trip and asked her to give his regards to Evelyn and Henry, she invited him to join her. No, she dared him to join her. And he said yes.

At dinner with Evelyn, Mary held court, every man there dancing attendance on her, even Tom to some extent. Henry was enthralled by her, which suited her purposes nicely.

After the meal, Henry suavely offered to walk her and Tom home instead of them taking a taxi. Tom beat a less-than-subtle retreat and took a taxi back, claiming he had a lot of reading to do. Mary let Henry walk her through the streets of London and kiss her in a rainstorm.

When she got back to Belgrave Square, Tom was still up, still in black tie, reading a paper and sipping whiskey in Rosamund's smallest, most intimate drawing room. He stood up, folding his paper, as the footman opened the door for Mary. She came in, peeling her gloves off and smiling like the cat that got the cream.

'Were you caught in the rain?' Tom enquired.

'Not too badly. We dashed for cover until it slackened off a bit.'

'How romantic,' Tom said, retaking his seat.

'Why are you playing Cupid?' Mary asked, half curious, half annoyed as she sat gracefully on the sofa, laying her gloves down beside her.

Tom sat back in his chair, legs crossed, whiskey in hand. 'He's nice, he's mad about you and he loves cars. I rest my case.'

'I don't see how it would work.'

'Why? He'll have to settle down eventually. Go into some sort of business. Why couldn't he do it from Downton?'

'I know, I-'

'He won't be as rich as you. He won't be as rich as your child. But he's a gentleman. And if I say that, it must be true,' Tom said, sipping his whiskey. 'Would you like a drink?'

'Just a tiny glass of whiskey and water.'

Tom got to his feet to go to the drinks table and fix her a drink. Mary rose to slip around the table and stand behind him.

'It won't work with Henry, you know.'

'Give him a chance. You never know what might happen.'

'But I do. Do you know how?'

He turned around to hand her her drink, his eyes widening slightly in surprise when he saw just how close she was standing to him. 'How?'

'Because when he kissed me, there were no butterflies.'

Tom gave her a quizzical look.

She moved closer to him, her voice low and sultry. 'You always gave me butterflies. Right from the start. You didn't even have to kiss me.'

Tom stared at her, barely moving a muscle, a rabbit in her headlights.

'You just had to look at me.' She leaned in, brushing lightly but deliberately against him to reach past and put her untouched drink on the table behind him.

'Sometimes, I just had to think about you,' she continued softly, taking his glass from his unresisting hand and setting that down too. 'And those butterflies would swoop around, driving me wild. And do you know the only thing that ever stopped those butterflies wreaking havoc on me?'

'What?' he whispered, powerless against her.

'You,' she purred, holding his gaze and moving closer still until there was barely an inch between them. 'You touching me. Your body against mine. You inside me. You filling me until there was no room left for those butterflies.'

Tom swallowed, his eyes never leaving hers.

'I've got butterflies right now, Tom. And they're driving me mad.' She slid her hand along the front of his trousers, cupping him through the fine material, relishing his sharp, indrawn breath. 'And this is the only thing that can calm them.'

'Mary…' he breathed, a faint warning in his voice.

She drew her finger lightly up his hardening length, making his whole body shiver. 'I want you to take care of my butterflies for me. Right here, right now.'

She slid her hands around his hips, under the vents of his jacket, grasping his buttocks, and slotted her body against his, pulling his groin tight to hers.

Tom groaned, his eyes briefly fluttering closed, then he seized her arms, pushing her back, back, back until she collided with the wall of the drawing room. He crowded her, flattening his body against her.

Mary gazed at him, unrepentant, her tongue flicking out lazily to lick her lips. Tom watched her do it and she saw his resolve break.

He bent his head, taking her lips in a hot, desperate kiss. Mary opened her mouth under his, letting him lick his way in, giving as good as she got. She felt his hands on her thighs, bunching up her evening dress, dragging it higher. Mary reached down, tearing at his fly to pull him free.

Tom's hands reached the curve of her buttocks and he gripped her, lifting her up and bracing her between his body and the wall. Mary wrapped her legs around him, pushing back against the wall, gasping as he dragged her underwear aside and speared into her.

She locked one arm around his neck and cupped his chin in the other hand, forcing his face up to hers so she could kiss him, hot, wet, uncoordinated kisses, as he drove in and out of her. She hung on to him tightly, pushing down as best she could to meet his strokes, revelling in the familiar push and pull between them.

'Mary,' he said, desperately. 'I can't… I'm going to… I…'

'Do it,' she whispered, fiercely, unable to take her eyes off his face as he rammed home inside her once more, and she felt his whole body stiffen as he emptied himself into her. She stifled the groan falling from him with her lips then slipped one hand between them to propel herself to her own peak. Tom shuddered against her as she flexed around him, thrusting several more times to help get her there. Mary buried her face in his hair, muffling her moans as she climaxed.

When she'd stopped shaking, he set her down gently, her back sliding down the wall until her feet hit the floor again, her evening dress slithering down her thighs to drape perfectly around her once more.

Tom refastened his trousers, keeping his head down, as Mary stood there, her eyes fixed on him. Eventually, he raised his head and looked at her.

'That was quite the seduction.'

'Thank you,' she said, seeing no point in denying it.

'I thought you'd put us in the past.'

'No.'

'But what about Henry?'

Mary stepped forward, laying one elegant hand on the front of his jacket. She put her cheek against his, her lips close to his ear. 'I don't want Henry. I want you.'

Tom closed his eyes, letting out a long, slow breath, tilting his head slightly towards her, as if waiting to hear what she would say next.

'And I mean to have you,' she continued, her voice low and intimate.

Tom didn't say anything, simply stood there letting her words sink in. After a few seconds, Mary pressed a lingering kiss to his cheek then walked away, making for the door.

'Mary.'

She stopped at the sound of his voice.

'I don't suppose you have your device in place, do you?'

She turned to look him in the eye from across the room. 'No, I don't.'

He gazed at her steadily, with an expression she couldn't quite decipher.

'I'll let you know if there are any consequences. Goodnight, Tom.'

Tom watched her leave the room, knowing he'd been thoroughly outplayed and not quite sure how he felt about it.