Yes, I know. It's the classic cliché. And you'd think I would be old enough and wise enough to know better, but I suspect we're all fools when it comes to matters of the heart. It's just that from the moment she first tripped into the meeting room, trailing highly classified files behind her, late for her first day and apologising in a voice made high by nervousness, I looked into those enormous, candid, aquamarine eyes, and I fell for her, hook, line and sinker. Most unusual, that, for someone like me.

You see, someone like me leads with their head, never with their heart. My head is a known quantity: a place of cool, rational, logical thought and factual analysis, full of patterns and codes, a safe haven of intellect and reason. With my heart, it is not quite the same thing, at all. Apart from my mother, I'd allowed no woman access in more than twenty years, not since Sarah had trampled all over it on her way out of our ill-fated engagement. My heart had since become a sad and shrivelled thing, or as T. S. Eliot put it so well, a rag and bone shop. My work kept me fully occupied, looking after Mum after Dad died took up the rest of my time, and I was happy enough, or so I thought. All that changed the day Ruth Evershed appeared on the Grid. It was a Tuesday, and raining. I remember thinking that her eyes looked like the ocean when it rains – huge, deep and the most extraordinary shade of blue, so pale in certain lights, they're almost green.

I know, too, that I'm not good with women – Sarah left me with a long and brutal list of my shortcomings in that department, quite confidence shattering, really. Designing spook gadgets, installing bugs, carrying out remote surveillance and making sense of bags of shredding lifted from someone else's office – these are things I am rather better at, if I do say so myself. Oh, and gardening. I love my garden. It's full of interesting plants. When Mum came to live with me a few years ago, my life became another cliché – the confirmed middle-aged bachelor, living with his elderly mother, doing an obscure Government job and pottering round the garden on a Sunday.

For more than a week after her arrival, I was so tongue-tied whenever I was near Ruth that even in team briefings I could barely speak, and then only in monosyllables. Well, I was never loquacious to begin with, so perhaps it went unnoticed by the others. Colin knew, but he would never have said anything. He was the soul of discretion, was Colin. I miss him, every day. And all the others who one day left the Grid, went out into the wide and dangerous world, and never came back, because they were far braver and more courageous than I could ever be. But I digress.

Ruth. She has become the heart and soul of Section D – everyone's confidante, the person who people go to for the difficult jobs, the ones which require her light touch and brilliant mind. Ruth brings people cups of tea, unbidden, just to cheer them up, and she always remembers to put a biscuit on the saucer. Nice ones, too, from her own personal supply of Hobnobs and custard creams. Ruth is kind to people, which is rare enough in our trade, and she is quite simply the best listener in the world. When Ruth listens, she stops whatever else she is doing and turns her gaze on you like twin blue spotlights, and she listens with deep concentration and total attention, as if she is now breathing in your words instead of the chill, dry air of the Grid. Sometimes she will tuck her hair back behind both ears, as if to hear you all the better. I used to think that if a bomb was to go off behind her while she was engaged in listening to someone, she would neither flinch nor turn until they had finished. That was in the early days, before I realised how things really were. Now, I still think that a bomb could indeed go off behind her and she wouldn't turn a hair, but let the Head of Section D so much as set foot on the Grid, and her attention would shift almost imperceptibly to wherever he was, even while maintaining her focus on whatever she was doing at the time.

An incident that I think of privately as the HM Customs Tea Party is probably where I should begin, chronologically speaking, a few months after Ruth joined our merry band. Some clumsy clot at HM Customs had managed to pour the entire contents of his capacious Arsenal anniversary mug of tea into a US diplomatic crate full of files while doing a bit of not-strictly-kosher snooping for Five, and of course the whole mess was duly delivered to me for fixing up. The tannins in tea are impossible to bleach or launder out of paper files, so I was facing a long night of file forgery, when Ruth came to see what that nice young Scottish girl, Sam, was talking about when she said there was a spot of bother with the crate.

Ruth's beautiful eyes sparkled briefly with amusement, then became darker and more serious as she assessed the damage, and the size of the job I ahead of me. "Tea?" she asked, more as a statement than a question. I groaned at the idea of letting any more liquid near the crate, then smiled at her. "I'm afraid so. Coffee, and we might have gotten away with it, but tea…" She smiled back at me and said, "I know, it practically screams English eyes in here have pryed. I've got a few things to do right now, but if you like, I'll come back in an hour and help with the copying?" I blinked in surprise – apart from Colin, it wouldn't occur to anyone to offer to help me. Not because they were thoughtless, but because I have always just gotten on with the job and delivered whatever was needed on time. I was sure that she was just making the offer to seem nice, but while I was trying to think of a gracious response, Zoe called for her on the Grid and she left me with a quick "I'll be back, I promise!" spoken over her shoulder.

And to my astonishment, she was. One hour and forty-five minutes later, to be precise, but she came back, rolled up her sleeves, and asked me where I wanted her, in a completely matter of fact tone, unaware of any innuendo. She's not that sort of woman, Ruth. She would have blushed to the tips of her ears, then fled the room, if she had realised it, or if I had said something suggestive in reply. Not that I would have – I'm hardly a seductive smooth talker, and such comments would have been flagrantly disrespectful even if I were – so I pointed her to the high-resolution photocopier, and set her to work making clean copies of the file contents, while I continued to compile them. Luckily we had plenty of the right sort of paper stock to hand - one never knows when one might be called upon to do a little forging of US government files, after all!

As we worked, we began to chat. Small talk mainly, the sort of thing which workmates talk about when they are getting to know each other. In our game, that sort of chit-chat doesn't come easily, because of the secrets we all keep, but I found that talking to her was easy. With her GCHQ background, she knew exactly what not to ask about, and so I found myself speaking with her as I would to a colleague of many years. She told me about her cats, about how moving to central London from Cheltenham had been harder on them than she had expected, and how she had always wanted to work for Five. I could see why – her mind is first rate, and coupled with her intelligence, she has a sort of intuition which often connects seemingly random events to come up with a compelling new analysis of the facts. I really don't like to talk about myself, actually I couldn't think of anything worse, but I wanted to make a favourable impression on this beautiful and kind person, standing in her stocking feet (she had kicked off her heels not long after taking up her station at the copier), painstakingly running top-secret US documents one by one through the machine, selflessly helping me when she should have left hours ago. So, I told her about this and that – how I had come to Five, where I had grown up, my favourite books, how I loved the seaside more than any other place – small talk, but I found myself wanting to tell her so much more.

Ruth was listening attentively, nodding in all the right places, when she glanced at her watch and then exclaimed at the time. "Oh no, it's after midnight! My poor cats will think I've abandoned them!" and apologising, she began to put her shoes back on, preparatory to leaving. She looked at me and realised I wasn't going to leave with her. "Isn't there someone you need to get back to, Malcolm?" she asked, her luminous eyes watching me as I continued to work, and then I said it. "Mum will have gone to bed hours ago, so no, not really. There was…going to be someone else, once, but it…well, no". I was appalled. Why was I telling her this? Why was I telling her that I was that thing that all sensible women fled, a man who lived with his mother, and one with an ancient, failed relationship, at that? Her kind expression didn't change as I faltered into awkward silence. She simply nodded, then said, "I'll see you on the Grid tomorrow, or should that be today?" and with a final smile, left me to my forging.