Mary felt like a small child could have knocked her down with the tiniest of feathers when Tom offered to take her to the racetrack at Catterick to watch Henry test a car. She wasn't sure quite what to make of it. It was, of course, entirely possible he just wanted to see the wretched cars, but at least it would give her a chance to talk to him away from prying eyes and sharp ears.

As she changed her clothes for the outing, her eyes fell on her jewellery box and she decided to send a silent message, pinning on the brooch Tom had given her at Christmas.

She saw Tom's eyes catch on the brooch as she walked to the car, but he said nothing, simply handing her into the car then going round to the driver's side and settling himself behind the wheel.

'It's good of you to come with me today but aren't we going to be rather early?' she said as he pulled off down the driveway.

'I thought we could take a small diversion to the spot I've picked out as a potential site for the repair shop. I'd value your opinion.'

'Ah, so a little business on the side.'

'Yes, if you're all right with that.'

'Of course, I am. Especially when it's all you appear to want to talk to me about these days.'

Tom was silent for a moment. 'I know we need to talk, Mary. And I know I've been-'

'Avoiding me?'

'- putting it off.'

'But why? Am I that much of a harridan?'

'No, no, of course, you're not.'

'No? Then why have you done everything you possibly can to avoid spending any time alone with me since you came back?'

Tom didn't answer, keeping his eyes on the road.

Mary stared at him, misery and anger churning inside her. 'Are you still not going to talk to me?'

'Yes, but not while I'm driving. Look, we're here.' He pulled the car over, steering onto a side road rising over a small hill. 'This is where I think we should put the repair shop.'

'Believe it or not, Tom, right at this moment, I don't give a brass farthing about the repair shop.'

He looked at her, his face troubled.

Mary put a gloved hand on his arm and felt him tense beneath her fingers. 'Tom, please. I don't understand what's happening here.'

He stared at her hand, then pulled away, opening the door to get out of the car and walk a few paces.

Mary followed suit, standing on her side of the car, waiting for him to say something.

'I can't do this anymore, Mary.'

She stared at him, biting her lip, masochistically needing him to spell it out. 'What, precisely, can't you do anymore?'

He met her gaze, an uneasy look on his face. 'Me and you. Our arrangement. I can't go back to how we were before I left.'

'I see.'

Tom waited, standing on the other side of the car bonnet, obviously expecting her to say more. Mary simply stood there, pale and silent, staring at him, determined not to help him end them.

'Aren't you going to say something?' he asked finally.

'You're the one with something to say. Not me.'

He looked down, seeming to find the gravel beneath his feet endlessly fascinating. 'I just, well, I don't know what you were thinking, but I don't think it's a good idea for us to pick up where we left off.'

'May I ask why?'

Tom looked at her, visibly uncomfortable. 'I don't think it's good for either of us. We both need to be able to move on with our lives, not trap ourselves in a difficult situation.'

Mary flinched. 'Is that what it was for you? A difficult situation?'

'No,' he said, forcefully, taking her by surprise. 'No, it wasn't… but I think that's what it will become if we start up again.'

Mary stared at him, trying to make sense of his words and failing.

'Why did you come back to Downton, Tom?'

There was a beat of silence before he answered her. 'Sybbie wasn't happy in Boston. She missed you all so much… and so did I. I underestimated how much this place has got under my skin. I mean, look around us. Look how beautiful it is. And peaceful. It's so quiet here. It's all Sybbie has ever known. She couldn't take to the city. It was too noisy for her, too dirty, too busy. She kept asking me when we were going home. In the end, I realised she was right. You were right. Downton is home now. And I never expected that.'

Mary felt a shard of disappointment pierce her heart that he hadn't mentioned them at all in his little speech. 'So, it was all about Sybbie then? Your decision to come back.'

'Isn't everything I do all about Sybbie?'

'Not everything, no.'

He looked askance at her.

Mary huffed out a small, bitter laugh, glaring at him. 'Well, you're not seriously going to stand there and tell me you took me to bed for Sybbie's sake, are you?'

Tom flushed. 'No, of course, I'm not.'

'No, you did that for you.'

Tom met her gaze. 'I did. And I don't regret it if that's what you think.'

'Right now, Tom, I honestly don't know what to think.'

He walked forward, bracing his hands on the bonnet of the car. 'Can't you see, Mary?' he said, urgently. 'Can't you see that if we just go on as we were, neither of us will ever be able to move forward? And you have a chance to do that now. With Henry.'

Mary looked at him, taken aback.

'Isn't that why we're going to Catterick today?' he ploughed on. 'You and Henry have this little dance going on, sounding each other out to see if you both feel the same. You're attracted to him; he's attracted to you. I know how it goes. You'll meet several times, flirt with each other and decide you want to take it further.'

'You don't know that.'

'I do, Mary, because I know you, and I certainly know what Henry is thinking. But you can't move forward with him if you start sleeping with me again. And I won't let you throw your life away like that.'

'But what if I want to keep sleeping with you?' she cried, her voice cracking.

Tom looked away from her. 'I'm not the only man who can scratch your itch. And, sooner or later, you'll need more than that. Henry can give you that.'

'You can't know that! You barely know the man! And neither do I!'

'I know he'll be good for you. I know he will challenge you and you need that. I know he can give you what I can't.'

Mary stared at him, tears pricking at her eyes. So, there it was. The nub of it. He didn't love her. He could never love her because he had loved her sister so much.

'Do you remember when we started this?' he asked, quietly.

She nodded, not trusting herself to speak.

'We made a pact. We said if one of us wanted to stop, we'd stop and go back to how we were. You called me naïve for saying we could do that. And perhaps you were right. But we have to stop, Mary. We have to stop and go back to being just brother and sister-in-law. And friends, I hope.'

Mary stared at him, feeling her heart breaking, and wondered bleakly where the man she'd fallen in love with had gone.

'It's for the best,' he said, sounding almost as if he were trying to convince himself as well as her. 'For both of us.'

With a Herculean effort, Mary pulled on her years of practice in hiding her emotions in public.

'You're right,' she said, schooling her face into a blank mask. 'We did make a pact and if you want to stop, then I suppose I will have to accept that. Now, we'd better go, so you can offload me to the man you've decided will be my next husband. I wouldn't want to inconvenience you any further.'

'Mary, I didn't me-'

'No, Tom,' she cut him off. 'You've said enough. Just take me to Catterick.'

Tom stood watching her as she got back into the car, sitting stiffly in her seat, then he got behind the wheel and released the hand brake, driving off with a heavy silence hanging between them.