Since Henry's departure for Birmingham and sharing her plan with Tom, Mary had relaxed considerably after the stress of the weekend. And things had changed a little between her and Tom, particularly in the office where they were almost guaranteed to be alone.

Although they stuck to their agreement not to begin a physical affair, Henry's behaviour had loosened Tom's strict rules. This week, they'd indulged themselves, allowing themselves more touches, more kisses. It was probably a bad idea, they both knew that, because it was getting harder and harder to stop when things became heated, but neither of them wanted to give up these little snatches of intimacy they allowed themselves.

As they got closer to the end of the week and Henry's return, Mary's tenseness returned. And Tom was delighted to discover he could ease her tension by trailing kisses along her neck and her jaw until she was twisting her head to meet his lips. But it was a dangerous game they were playing. The more intimate they became in private, the more difficult it would be to hide their feelings or not give themselves away when they weren't alone.

Friday found Tom at the dealership. Ideally, he'd wanted to be at Downton ready for Henry's return, but an appointment with a client and an assessment of the mechanical skills of a would-be apprentice had him in York.

As he caught up on paperwork, the telephone on his desk began to trill insistently. Tom scribbled the running total for the account he was billing on his notepad then picked it up. 'Talbot & Branson Motors. How may I help you?'

'May I speak to Mr Talbot, please?' a voice with a slight Brummie accent said.

'I'm afraid Mr Talbot is not here at present. This is Mr Branson. May I help you at all?'

'Perhaps you could pass on a message to Mr Talbot, sir, if you would be so kind. This is the Royal Midlands Hotel in Birmingham. I'm calling to let Mr Talbot know housekeeping found a bracelet in his room, which we believe Mrs Talbot may have dropped during their recent stay with us.'

Tom went still. 'Mrs Talbot?'

'Yes, one of our chambermaids found the bracelet under the bed when she was cleaning the room after Mr and Mrs Talbot checked out this morning. It appears to be of some value, so we'd like to reassure Mrs Talbot it is in safe hands.'

'Right, thank you. That's very good of you. I'm sure Mrs Talbot will be very relieved to know that,' Tom said, the words sticking in his throat.

'If you could ask Mr Talbot to telephone us, we'll be delighted to make arrangements to return the bracelet. The number for the hotel is on our letterhead on Mr Talbot's bill.'

'I'll be sure to ask him to contact you. Thank you for calling,' Tom said.

'Thank you for your assistance, Mr Branson. I bid you a good day,' the hotel employee said, ending the call.

Tom hung up the telephone and sat there, his head spinning with the realisation that Henry was having an affair.

He clenched his fists, thinking about it. Henry's purpose in Birmingham was to talk to a number of car manufacturers about Talbot & Branson Motors becoming authorised suppliers of their vehicles. He was there for legitimate business reasons, but it appeared now that not all his business there was above board. Mr and 'Mrs' Talbot had stayed at the Royal Midlands Hotel. And Tom knew for a fact that Mary had not left Downton this week.

He closed his eyes as white-hot anger shot through him. He thought of everything he and Mary had done, the sacrifices they'd made to stay away from each other, the lengths they'd gone to to avoid temptation, the heartbreak they'd endured to avoid betraying Henry. And yet now, it appeared, Henry was cheating on Mary, making a mockery of both their marriage and of the actions Tom and Mary had taken to make sure they did not betray him.

This turn of events would be good for Mary's plan to extricate herself from her marriage, he knew that. It might even hasten the end of it. It was a good thing, he told himself. But suddenly Tom found himself praying that Henry did not return any time soon because if he saw his business partner in the next few hours, he wasn't sure he could be responsible for his actions.

Henry breezed into the office at the back of Talbot & Branson Motors on Friday afternoon some three hours after Tom had discovered his secret.

'Ah, Tom, you're here. Excellent,' he said, smiling broadly at his partner. 'I can bring you up to speed with the discussions I've been having. It's all looking very promising.'

'It was a productive week, then?' Tom said, rising to his feet, his gaze fixed on Henry.

'It was indeed. It looks like I might have to go back down there over the next few weeks to seal a few deals, but it's all looking good for us.'

'And will you be staying in the same hotel?' Tom asked, in a clipped voice.

Henry looked askance at him, nonplussed by the question. 'Possibly. It was quite a nice place. Very decent breakfast.'

'Yes, and the staff there are very honest.'

'Have you stayed there?' Henry asked, dropping his hat on his desk and looking over at Tom in surprise. 'I don't remember you going to Birmingham.'

'No, I haven't, but one of them called this morning to inform you they'd found Mrs Talbot's bracelet under the bed after you and she checked out yesterday,' Tom said, his voice stony.

Henry went completely still. 'Ah.'

'Ah?' said Tom, feeling his temper begin to boil. 'Ah? Is that all you've got to say?'

'Well, obviously, this is not ideal.'

'Not ideal?'

'It's not ideal that you know about this.'

'You think that's the problem here, Henry? That I know about your infidelity?' Tom asked, incredulously. 'Because if you think that's the problem, you're sadly mistaken.'

Henry shifted into appeasement mode, laying on the charm that usually got him out of scrapes. He sauntered over to Tom, hands spread wide in a pacifying gesture. 'Look, old man, I know this looks bad, but it's not a serious thing. It's just a bit of fun when I'm out on the road. It doesn't mean anything.'

Tom felt his precarious grip on his temper become shakier. 'It doesn't mean anything?' he bit out.

'No, Tabitha knows the score. She knows I won't leave Mary.'

Tom stared at him, the cogs whirring in his mind as he realised what Henry had inadvertently just told him.

'Tabitha. Is this… is this a one-off thing, Henry, or is this Tabitha your mistress? Because it sounds like this has been going on for more than a few days if she "knows the score".'

Henry bit his lip, looking away from Tom as he realised his mistake.

'Well?' Tom said, his voice as hard as flint.

'I've been seeing her on and off since I started visiting Birmingham. She's one of the secretaries to the top brass I've been talking to at Austin,' Henry said, reluctantly.

Tom stared at him, feeling the ball of anger in his chest expanding. 'How long?'

'I don't think that really matters, does it, old boy? You don't need the details.'

'How long?' Tom repeated, through gritted teeth.

'Just over a year or so,' Henry admitted.

'A year,' Tom echoed, thinking how Mary and Henry had been married for just short of two years.

'But as I said, it doesn't mean anything. She's just an outlet while I'm away. And Mary's been… well, I won't go into that, but Tabitha's been a welcome respite just lately.'

'Mary's been what?' Tom said, immediately on his guard.

'Well, I probably shouldn't say because this kind of thing should normally stay between a man and his wife, but under the circumstances, I'll tell you, so you'll understand. Mary's been somewhat reluctant – unforthcoming, shall we say – in the bedroom department in the last month or so.'

Tom punched Henry, socking him hard in the mouth, sending him clattering down onto the floor.

'What the deuces, Tom?' Henry shouted angrily, glaring up at his furious partner from his prone position, touching his thumb to his bleeding lip.

Tom rocked on the balls of his feet, flexing the fingers of his right hand as the shock of the punch still reverberated up his arm. 'You bastard!'

Henry scrambled to his feet, holding his hand out to ward Tom off. 'All right, all right! Calm down. Christ, I didn't think you'd take it this badly. I thought you might understand. I mean a man has needs, you know that.'

'Understand? Understand? You've been cheating on Mary for a year! Why would I understand that?' Tom yelled, murder in his eyes.

'That's not how I'd put it,' Henry said, wincing as he touched his bloody lip again.

'No? How would you put it then?' Tom snarled.

'I look at it more like I'm saving her from having to perform her wifely duties too often if she's got to that age where women don't like doing that sort of thing anymore,' Henry said, trying to keep his tone reasonable so as not to provoke Tom any further.

Tom stared at his partner in utter disbelief, itching to hit him again. He wanted to put him straight about Mary's carnal appetites, but he knew he couldn't without revealing what had been happening between himself and Mary. Instead, he shook his head.

'You're a fool, Talbot. You had the best woman I know, and you've betrayed her.'

'Had?' Henry frowned, shaking his head. 'The last time I checked, I still have her. She's still my wife.'

'But for how much longer when she finds out what you've been up to for the last year?'

'No, no, you can't tell her, Tom. She doesn't need to know. What she doesn't know won't hurt her,' Henry said, a hint of desperation entering his voice.

Tom shook his head, glaring at Henry. 'She needs to know what an unfaithful bastard she's married to.'

'Why? Why does she? What purpose would it serve? She won't divorce me, you know. She couldn't bear the scandal. And the family won't want that, their precious name dragged through the mud. Better that she doesn't know, then she won't have to even think about any of that.'

'She needs to know. She needs to make that choice herself. You don't get to make it for her,' Tom said, coldly.

'No, Tom, please! Don't tell her. It's nothing serious. And anyway, what makes you think she'll believe you?' Henry said, his desperation growing.

'She'll believe me,' Tom replied, utter certainty in his voice.

'And you're ready to be the one to hurt her like that, are you?' Henry challenged.

Tom's eyes flashed with anger, making Henry take a step back. 'It's not me who's hurting her!'

'And why is this any of your business anyway?' Henry scowled. 'This is not your marriage.'

'No, if I were married to Mary, I would never have done this to her!' Tom shouted, furious with his partner. 'Never!'

Henry paused, narrowing his eyes at Tom. 'Ah, right. I see. It's all making sense now.'

'What do you see?' Tom spat out.

'I see you, Tom. Your real motive for telling her. You love Mary.'

'Of course, I do! She's my sister-in-law!' Tom retorted, feeling a sliver of panic rising up inside him that he might have revealed too much and be jeopardising Mary's plan.

Henry gazed at him thoughtfully. 'No, it's more than that. You love her. You're in love with her.'

'Don't be ridiculous,' Tom said, turning away from Henry.

'No, you do. You love her. All these years, I've thought it was just friendship you felt for her, but it's not, is it?'

Tom said nothing, stalking over to his desk, shoving papers into his briefcase.

'Is that what that weird estrangement between you two a few weeks ago was about? That period when you were suddenly and mysteriously working from here all the time and she was on her own at the Downton office? Did you try it on with her? Did she banish you? Is that it?' Henry speculated.

Tom shook his head angrily, not looking up from his briefcase.

Henry watched Tom carefully, furrowing his brow as he thought about it. 'Did you want more from her than she was prepared to give? Did she slap you down and put some distance between you? Is that what's been going on? Because I know something was.'

Tom stopped what he was doing and glared at Henry.

Henry stared back at him and nodded. 'I'm right, aren't I? Poor old Tom, eh? Cast aside because he over-reached. And now you want to lash out by telling Mary about my little indiscretion. Really, I never took you for a small man, Tom. And you're hardly in a position to judge me if you've been trying to get into my wife's knickers yourself. By rights, I should be punching you.'

Tom turned to the coat rack behind him and yanked his coat off it, putting it on in silence before turning back to face Mary's husband, ice-cold fury running through his veins.

'You can think what you want, Henry. I don't care. But you're right about one thing. I do care about, Mary. I care about her deeply, and if you don't tell her about your "little indiscretion", I will.'

With that, Tom rammed his hat on his head, picked up his briefcase, and walked out of the office, leaving Henry staring after him, blood dripping from his lip onto his white shirt.