On the last day of the summer term she returns to her flat buzzing with happiness. Her first year at Sulgrave Heath had been an unadulterated success. The students were bright, eager to learn and now treated her as if she'd been a fixture at the school for years. There had been some exceptional results in her language classes and her choir had won a county competition. And when the Independent Schools Inspectorate had come in during the spring term her lessons had been described as 'outstanding'. When Caroline had told her the news there had been an unmistakable note of pride in her voice.

Even her relationship with Caroline had gone well, in that they had managed to stay out of each other's personal lives while remaining on good terms at work. There had been no more visits to each other's flats but she occasionally found an informal note on her front door, one offering her some steaks because she'd had 'a moment of madness' in Waitrose and couldn't fit them all in the freezer, another thanking her for all the hours she put into the choir and saying how much William had enjoyed singing in the competition.

As the year went on, though, she'd become a little puzzled. William was a regular visitor to the flat and she sometimes ran into him on a Sunday. Lawrence visited too, less frequently but with much more noise, and she'd even met Caroline's mum, an instructive event that had explained a great deal about the origins of Dr Elliot's natural air of authority (although she rather thought it tipped over into superiority in Celia's case).

But she never, ever saw John. Which wouldn't be much of a mystery if Caroline went to stay with him at the university, but as far as she could tell she hadn't spent a night away from home the entire year. What kind of marriage was that?

Whatever was happening, it was clearly none of her business, but she couldn't help but be intrigued. Was this why Caroline was so keen to be neighbourly, to establish a basic friendship – because she knew that whoever lived next door would put two and two together and realize that all was not as it seemed?

The main thing though was that she had built a friendly but professional relationship with a woman who had, to be frank, scared her at first, so that was another success and another reason to think that coming to Sulgrave Heath might well be the best decision she ever made.

Sinking gratefully into her sofa she thinks of the weeks of holiday ahead of her and starts making plans. Ten minutes later she's still happily day-dreaming when she hears the front door bang downstairs; Caroline's home. She wonders briefly what Dr Elliot gets up to in the summer holidays and then goes back to visions of weekends in Barcelona with her friends and evenings at the theatre.

And then she hears it. The unmistakable sound of a woman's sobs.

For 30 seconds or more she's indecisive. Every instinct in her heart is telling her to go and comfort her, but her head is far more circumspect – apart from anything else, she might tell her to sod off and give her some privacy.

One more wracking, heart-wrenching sob later and she can't stand it anymore; she steps out into the hallway, finding Caroline slumped on the floor having not even made it to her flat.

"Are you all right?" she says stupidly, kneeling down to get closer to her. Caroline meets her eyes but can't seem to stop crying.

"What's happened, what is it? Are you hurt?" Her boss shakes her head miserably, swiping ineffectually at her tears.

"Come with me," Kate says firmly. "Come inside and sit down."

To her surprise Caroline meekly does as she's told, taking hold of Kate's hand and allowing herself to be pulled upright and then led into the flat. They sit together on the sofa and Kate's about to start asking questions when Caroline dissolves into sobs again.

"Oh Caroline, come here." Reaching forward she pulls her into her arms. There's no resistance at all and she feels her lean her head on her shoulder and give in to the crying. Kate holds her firmly, arms wrapped around her, too eager to ease her pain to worry about awkwardness. At the back of her mind she's aware of her body heat, the soft curves pressed against her own, but the seriousness of the situation keeps her thoughts from wandering into dangerous territory.

It takes another few minutes for the sobs to stop completely. When they finally die down Caroline withdraws from her embrace but stays close to her on the sofa; Kate offers her a box of tissues.

"Sorry," says Caroline, making a face. "How ridiculous."

"Not ridiculous at all."

"You'll think it's perfectly ridiculous in a minute."

"Will I?" she says, puzzled. "I find that hard to believe."

Caroline takes a few deep breaths, blows her nose several times and wipes the remaining tears away.

"Nothing's happened. I'm crying over nothing."

"Obviously something happened."

"Child grew into adult is what happened. Nothing. Ridiculous."

"I wish you'd tell me properly."

"William's gone to summer school, I was seeing him off. For six whole weeks. And then he'll be at Oxford and then he'll have his own life and his own family and they never really come back, everyone says so. So that's it now, my boy's gone forever."

Unexpectedly she finds herself moved. Say what you like about Dr Elliot but she was clearly a wonderful mother.

"I bet he'll be back all the time."

"Doubt it."

"Really, I'm sure he will. He'll bring his washing."

She snorts and then covers her mouth in embarrassment.

"And he'll be ringing all the time for more cash. And he'll need someone to show him how the oven works, and what a stopcock does, and what you're supposed to do when your girlfriend says there's nothing wrong but there obviously is. He'll be home all the time, you won't hear the end of it. You'll wish he'd gone to St Andrews."

A small smile is creeping onto her face; the tears have dried up.

"What's the answer, to the girlfriend thing?"

"Oh God, buggered if I know. One of life's little mysteries."

The smile's in full force now; it feels lovely to have cheered her up so much.

"You really think he'll come and see me?"

The vulnerability in her voice is so evident that she has to swallow down a lump in her throat.

"Of course he will. He's come home most weekends hasn't he, even though he's in dorms? What does that tell you?"

"Oh no. Sunday lunch. I do the full roast dinner, all the trimmings, have done for years, it's always been his favourite meal. And there's going to be no-one there to eat it now. Lawrence never comes on a Sunday because of his matches. It'll be me and a cheese sandwich and Songs of Praise."

"Well that doesn't sound like much fun. How about you make it for me instead?"

Caroline stares at her; she hopes she hasn't gone too far. But the thought of her vulnerable and alone is surprisingly poignant.

"Would that…would that be all right?"

"All right? I haven't had a proper roast in years, I can never be bothered to make it for one person. You'd be doing me a massive favour."

"If you're sure it's not imposing?"

"Of course not!"

"Then that would be lovely, thank you. About 1.30?"

"Sounds great. And I should be thanking you, you know."

"Good. And thanks for…you know. Listening. Not treating me like a mad old bat."

"Anytime."

Caroline stands up and they walk over to the door. Kate briefly wonders whether to hug her goodbye, but she seems so much more self-contained now that she's not quite brave enough to try it. Instead they smile at each other and Caroline touches her on the arm slightly awkwardly before heading down the corridor.

Two days later and she's sat on the sofa in Caroline's living room after a truly delicious roast lunch. Their conversation has flowed surprisingly freely, despite – or perhaps because of – Caroline's minor meltdown. Maybe she'd been wrong about the whole personal versus professional situation. Maybe they could become a little closer than that and still make it work.

"You've been happy in the flat?" Caroline asks.

"Oh yes, it's really nice. Not nice, actually, wrong word entirely, it's beautiful, definitely the most attractive place I've ever lived in."

"And I hope the…geographical disadvantages haven't been too difficult to cope with?"

She smiles at her, spotting a real note of concern on her face. "Not at all."

"Only the staff were not at all keen on the idea, it was left empty for a year because we were struggling to find someone to take it up. It's an odd little place really, my understanding was that it was established years ago as a flat for the deputy headmaster, presumably back in the days when such gentlemen were bachelors or always sent their own children away to school.

"But now it's too small for anyone with a family, anyone with a goldfish, to be frank, and Mr Michaels has four children so it would never have done for him. It was perfect for the previous deputy, Mr Burton, but he retired of course, and then it was offered to all the existing staff in order of seniority but no-one wanted it. I was beginning to feel rather unloved."

"I'm sure it wasn't because of you."

"Oh come on now, I think we both know better than that. Even the staff who already live on site turned it down and I don't blame them, I don't think I would have volunteered for it in their position. I'm not sure what we would have done with it, it might have been the most aesthetically pleasing broom cupboard in the world."

"Well I was very pleased to get it."

"Kate, I wanted to…I wanted to mention, to say that…it had been a bit of a concern of mine, that flat. And you have been a model of discretion and I wanted to thank you. I think you know what I'm referring to."

She hadn't expected her to ever bring it up; she chooses her words carefully.

"There are no thanks required, Caroline, I assure you. Your personal life is exactly that, personal, it's nobody else's business."

"Ah, but that's where you're wrong, you see. It would be the biggest scandal at Sulgrave Heath since Mr Campbell had a bit of a breakdown and started teaching Year 9 that the world was run by lizards."

"He taught…never mind, that's not important. But I don't understand why…I mean, surely…obviously I don't know the details, but it's hardly a scandal, is it?"

"The details are the scandal."

She looks so sad all of a sudden that Kate reaches out to her without thinking, taking her hand. Caroline squeezes gently as if to thank her.

"If you want to tell me, I'm here to listen. And if you don't, I won't ask again."

"It's very simple, really. There were affairs."

"Oh Caroline, I'm so sorry. That's awful, I'm sorry. But…is that really so scandalous, in this day and age?"

"Affairs, Kate. Plural. The devil's in the details."

"I'm sorry, I'm not sure I…"

Caroline's looking straight at her, her gaze piercing, her eyes a shining blue, and suddenly she understands.

"Oh! Oh, I see."

"I've disappointed you."

"No, no, of course not, of course not."

"I can see it in your face. You don't approve."

"It's none of my business." She tries to keep her face as neutral as possible; she's not really sure how she feels about this.

"I don't approve either, by the way, not at all. I never thought I'd be the type of person who…in my defence, it was John's affair that came first, I could never have been the first one to…I found out about it and went a bit mad, I suppose, and ending the marriage would have been so fraught with difficulty, with the boys and my job and all the bloody gossip. And there was someone who I cared about, who was pursuing me, I'd been trapped in this dead marriage for years, and eventually I sort of…surrendered. Technically we were separated already, well, we were separated, but it still should never have happened. It's not something I'm remotely proud of."

"I try not to judge people, I promise. Could you not have divorced him though, made a clean break? I understand it being hard on the boys but surely they would been OK. And the gossip would have died down pretty quickly, wouldn't it?"

"Another salient detail. The trouble with a divorce is that it tends to open the floodgates, it's a spotlight on your personal life and everything is revealed. Tiger Woods drives into a lamppost and suddenly all his peccadillos are on display."

"But I still don't see why it would be such a scandal, I mean, people understand a failed marriage, the complexities of relationships, even affairs, they really do, it's not the 1950s, you could have-"

"She was a woman. My lover. My affair. We both had affairs with women."

For a moment she thinks she's misheard, misunderstood, but there can be no other meaning to her words. She takes a breath, giving herself time to absorb the information, acutely aware that they're still holding hands.

"Gosh. Well. I'd love to tell you that I think you're wrong, but I don't think I can. I don't think it's a full-blown scandal but it would certainly be serious gossip. It must have been so hard for you."

"It hasn't been a whole bundle of fun, that's for sure."

"So…what's the plan? You can't leave things like this forever, can you?"

"John's prepared to give me a divorce but only if he gets shared custody of the children, and I won't have that. They already go to stay with him for some of the holidays, I don't want him throwing his weight around the rest of the time. He might not get his way of course, from what I can tell he probably wouldn't but as long as he's contesting the divorce there's a chance. And that's on top of the fact that he'd use the affair against me and everyone would find out about it and gossip for England and Christ knows what would happen with my job. The governors of a school like this want a respectable headteacher and that means heterosexual and married, whatever diversity bullshit they might spout in their board meetings. So if I wait until Lawrence is old enough-"

"It won't matter what John wants, the boys will be adults. And then he won't have a reason to contest the divorce."

"Exactly. And then it's just possible that we can get through the whole process without all the dirty laundry being aired."

"God, Caroline. Have you…does no-one else know about this, you've been coping with it all by yourself?"

"I'm not a child Kate, I'm perfectly capable of tying my own shoelaces."

Instinctively she draws her hand away, her arms covering her body defensively.

"Shit. Sorry. That was a reflex, I hate being told I need help."

"I didn't say you needed it."

"I know. Sorry. Forgive me. And no, no-one else knows about it, so I'm not used to talking about it which is why I fucked it up just then. Sorry."

She relaxes slightly. "You shouldn't swear, Dr Elliot. Think of the children."

"The children aren't here. And if you mean the pupils, they all swear like sailors."

"Think of me, then. I'm very young and innocent, you shouldn't corrupt me."

"Well OK then. Do my best," she says, smiling at her.

"So…is your…your lover, are you still-"

"Oh no, no, that was all done and dusted a couple of years ago."

"I'm sorry to hear that."

"It probably wouldn't have lasted, it was more about…hmm. Probably shouldn't finish that sentence!"

"It was more…what?"

"Doesn't matter. Highly inappropriate topic." A blush has started to creep up her neck. She looks so embarrassed that it can only mean one thing.

"Were you going to say 'More about sex'?" she says in astonishment.

"I was going to put it far more delicately than that. And I thought you said you didn't judge people."

"I don't, I'm not…" she stammers.

"It didn't start out like that, I didn't go looking for some tawdry…I didn't go looking for an affair and I certainly didn't sleep with someone just for the sake of it. We were friends, I cared about her and then it developed and I thought it could be something serious but as it turned out the most compelling element happened to be the physical. That's all."

There's a defensive note in her voice but her chin is raised, her gaze steady – she's not exactly apologetic. And why should she be? She feels that spark of attraction again, stronger this time. The idea of her in bed with another woman, exploring her body, touching her…the idea of her enjoying sex, loving sex…she clears her throat and tries to clear her mind of the arousing images that have appeared unbidden.

"I've made you uncomfortable," says Caroline.

"No, no, it's…not at all. I'm glad you trust with me it. And why on earth shouldn't you…enjoy…"

She trails off awkwardly; Caroline's studying her now and she can almost feel her gaze on her skin. It's not helping her flustered state; she's aware of a blush beginning to creep up on her as the arousal fails to dissipate.

"I really have made you uncomfortable. I apologize."

"There's no need, Caroline, really. I'm not a prude about these things, it's just…well, if you'd asked me what topics of conversation we were going to cover today, this probably wouldn't have been one of them." She laughs nervously, wondering if her excitement is as obvious as it feels.

"We should move to safer ground. Let's talk about you for a while, it's very rude of me to keep burbling on about myself."

"OK," she says. "Sure."

"So how's your sex life?"

She stares at her in shock for a few seconds before bursting into laughter. "Oh I am definitely not answering that question."

"No luck, then? Not so much as a snog?"

"Caroline Elliot, will you kindly leave me alone. I am not talking about my sex life or lack thereof with my boss. I did you a favour, remember, trekking all the way over here and eating your delicious roast, the least you could do is talk about the weather."

"Fine, fine, message received loud and clear. You're quite right, of course, I should never have got us onto this, I'm not even sure how I did. I shall restrict myself to more appropriate topics."

They grin at each other, a sparkle dancing in Caroline's eyes. She really is beautiful. Kate had noticed her attractiveness before, of course, but there's something about this open, teasing Caroline that's beautiful in a very different way to the authoritative charms of Dr Elliot.

Caroline looks at her watch, none too subtly; perhaps it's time to go. She fights against a pang of disappointment.

"Is it getting late, I should-"

"Oh no, no, sorry, it's not that, only…well. Promise not to laugh?"

"Um…OK."

"It's almost time for Songs of Praise. I make fun of it but I do quite like it, William would tolerate it because he liked the hymns and it became a kind of tradition, not that we're religious but it did become our thing. It goes without saying that you'd rather gouge your eyes out with a spoon but-"

"Let's watch it. I don't mind, I like Aled Jones."

"Are you sure it's OK? It reminds me of William and…"

She trails off, a sadness appearing in her eyes. Kate wants to reach out and take her hand again but she's keenly aware of the change in the dynamic between them, so she keeps her hand to herself and smiles sympathetically.

"Put it on, really."

"Thanks, Kate. You're very kind."

The television is brought to life and Kate settles back on the sofa, grateful for a chance to regroup, letting the programme wash over her but really thinking about the woman she's sitting next to and how little she really knows about her. An enigma, she thinks. Sitting there with her slippered feet propped on the coffee table, humming along to the Songs of Praise theme tune, right after admitting to an adulterous affair that was mainly about lust. Scaring the life out of a pupil from 30 paces and being so sensitive that a few careless words can pierce her heart. Fiercely independent and so lost without her son that she longed for companionship.

Definitely an enigma. And she was definitely intrigued.