Almost a week passes before I see my chance; a week of watching and waiting as Ruth turns up to work, does her job with her usual diligence, and then leaves, looking neither left nor right as she steps through the pods. She is as efficient and as terrifying as an automaton, bowed under her burden of guilt and grief; and added to this now is the weight of Harry's solicitous regard for her. At another time, perhaps Harry's attentions might have been welcome, but in her current state of mind, she actively avoids him, disappearing off the Grid at odd moments. I notice that she no longer sits at his right hand in briefings, nor spontaneously bursts into his office, nor glances across the Grid at him. Instead, she withdraws behind her walls of glass, and sinks ever deeper into a private world of sorrow.

It is almost more than I can bear to witness, and I am not alone in noticing the change in her demeanour. Zaf, unsure of what else to do, brings her treats from the trendy South Bank cafés he likes to frequent at lunch; little cakes, fruit tartlets and other sweetmeats appear on her desk, only to disappear into the dustbin at the end of the day. Adam watches her closely, but keeps his counsel, perhaps waiting for her to speak first; he is Fiona's husband, after all, and only too well aware of the delicacy of the situation. Two officers were under threat of death; one lived, the other died – and how can the survivor begin to confront the loss of their colleague, let alone the grief of the rest of the team? Harry's reaction to Ruth's distancing behaviour is predictable; he responds in kind, becoming taciturn and gruff with the rest of us, and strangely awkward in her presence. He spends a lot of time at Whitehall, no doubt keeping tabs on Juliet Shaw, our new national security coordinator, and the level in his whisky decanter drops alarmingly, day by day.

Even Colin is more than usually attentive to Ruth, prioritising her tech support requests, offering to help her catch up on the backlog of routine surveillance reports which has built up during the Shining Dawn operation; and it is Colin who broaches the subject of what to do about Ruth with me. He picks his moment with impeccable timing, while the two of us are working in the server room, late one afternoon, running diagnostics. We are alone, and unobserved by the internal security cameras. "Malcolm?" he begins, more diffidently than usual. I slide out the rack of the switching hub I am working on, and raise an enquiring eyebrow. "Look, tell me if I'm out of order here, but how is she? Ruth, I mean. She's been very quiet, since Danny's funeral. Is she alright?"

I stare at him, shaken by his directness, before I shrug my shoulders and reply, "I really don't know. She was very upset by Danny's death, of course, and then Shining Dawn happening so soon after…it's an enormous amount to take in, all at once." Colin frowns, and then steps over to where I am working. "When you went to sit with her at the funeral, you pretty much blew your cover, with me at least. So come on, talk to me. How is Ruth? And just to be clear, I'm asking because I'm worried about you. You've hardly said a word this week." I look at my best friend, and the temptation to unburden myself is almost overwhelming, until I remember my father's words…To earn someone's confidence, you must first learn to keep someone's confidence; never talk about anyone behind their back, son…it is a principle which has served me well in this life so far.

"Well, I'd be lying if I didn't say I was concerned for her, as a friend. But I don't really know any more than that. She hasn't spoken to me about it, and if even she did, I'd hardly be in a position to discuss it." Colin nods, his eyes large and serious behind his spectacles, then he reaches out to squeeze my shoulder affectionately. "You wouldn't be you, if you did. You've got integrity. Good luck with her, and if you ever do need to talk about it, we'll go out for a pint somewhere, yeah?" I blush with faint embarrassment at this unusual display, before we both turn back to our work. True friends, such as Colin, are few and far between, especially in our trade, and I know that he means every word he says, but I can't risk it, not where Ruth is concerned. As I methodically work my way down the next router tower, it occurs to me that Colin has just told me that he accepts my relationship with Ruth, in whatever form it may take, despite his previously stated misgivings. Far from feeling anxious at this thought, it is as if a pressing weight on my shoulders has fallen away. If only Ruth would agree to telling a few key people about us, I think, how much easier it would make things. Harry, for one, deserves to know the truth, even though the idea of actually telling him still fills me with irrational dread.

When my hands begin to grow clumsy in the chill air of the server room, I decide to step out into the service corridor which runs behind it, rather than back onto the air-conditioned Grid; I need a few minutes at an ambient temperature to restore my circulation. Stepping out of the rarely-used back door of the server room, I nearly trip over Ruth, who is sitting with her back to the wall next to the door, holding a mug that I recognise as Danny's with one hand, while she tents the other over her eyes. She is perfectly still, and it is not until I crouch down next to her, my knees cracking in protest, that she gives any indication that she knows I'm here at all. "So this is where you've been hiding," I say softly, as she turns her head to look at me out of red-rimmed eyes.

My heart lurches as I see the tear-tracks on her cheeks, and hear her sniffles; she has been sitting out here, alone, crying, and for quite some time, I deduce by the sodden tissues in her lap. Reaching into the inside pocket of my suit jacket, I pull out my unused handkerchief and hand it to her with a half-smile. "Mother was right, it seems – never leave the house without a clean hanky." Ruth takes it gratefully and dabs at her face, still snuffling, while I shift position to sit next to her, leaning against the server room door. We sit in silence for a while, not looking at each other, just being together, and eventually I feel her move closer to me; I almost hold my breath, as she tilts her head against my shoulder, and sighs shakily. This is the closest we have been in weeks, since the weekend of the Midsummer Ball, in fact, and it is wonderful just to re-establish physical contact, however tenuous; just for this moment, her walls are down, and she is here again, with me.

Eventually, she begins to speak, her voice ragged from crying, "I was unpacking the dishwasher in the tea room, just for something mindless to do, and I found this…someone must have been using it without knowing whose it was…as soon I saw it, I had to get out of there…Danny never let anyone use his mug, not even Zoe…I miss him so much, Malcolm…" I put my arm around her shoulders, and draw her closer. "I know, my darling, I know." "I don't know what to do with it all, all the sadness, all the guilt…I feel like it's pulling me down, and I'm drowning in it…" I turn to look at her, so small, huddled into herself, and I am filled with pity for her. "What can I do to help, my love? Tell me, what do you need?" She answers straight away, "I hate being alone, when I go home…it's so lonely, and everything seems so much worse at night…" I understand exactly what she is talking about; the black dog hunts at night, finding the broken, the lonely, the sad and the sorrowful, and latching on fiercely.

I take a deep, steadying breath - carpe diem… "As it happens, Mother is away for a few weeks… would you like to come and stay with me?" Her eyes scan my face for a long moment, before she gives a tiny nod, and says, "Just for a couple of nights? I couldn't leave the cats longer than that…" I can feel my face threatening to crack into an ear-to-ear grin as I register her reply, even as my back begins to protest. Groaning, I climb to my feet and offer her my hand, pulling her up gently. We briskly brush concrete dust from each other's backs, my heart racing as our hands skim over each other; there is a breathless instant when our eyes meet, and she says, "I could come over tonight, if that's all right…" My answering smile must say everything, as my heart is too full for speech, because the next thing I hear is, "Around nine?" as she turns and walks away, down the corridor. I step back into the server room, and as soon as Colin sees me he says, "I'll finish up here, if you've got something else to do?" his tone carefully neutral, but his face telling me what he is really thinking. I check my watch – it's six-thirty p.m., and for once, I decide to take Colin up on his offer. I need to get in some supplies, I need to make some preparations; I need to go, but first, I need to erase the last twenty-two minutes of security footage from the camera outside the server room door…at least, if our relationship was out in the open, I wouldn't have to keep doing this…fortunately, the security staff never conduct live surveillance on the service corridors!

Two hours and fifteen minutes later, after a hurried visit to Fortnum's before rushing home to check over the house, put fresh sheets on my bed, and make up a guest room, in case Ruth just wants her own space, I have changed out of my suit and am standing in my dressing room, wondering what to put on. Ruth has only ever seen me in suits at work, or white tie (or nothing at all, a primal part of my brain whispers), I realise, as I contemplate my options, which aren't many – I really don't have much call for an extensive wardrobe. Eventually, I settle on summer-weight khaki trousers, and a Tattersall check shirt. Hardly a picture of sartorial splendour, I know, but I don't want Ruth to think I live in a suit. Next, I conduct a final spot check through the house – fresh flowers in place, yes, wine chilling, yes, clean towels in the bathroom, yes… before sitting down to nervously await her arrival, as full of apprehension – what will she think of my home? – as I am of anticipation.

As it happens, I choose to sit down on the bench of the old upright piano my mother insisted on bringing with her from Wales, and almost without thinking, I lift the lid, looking at the yellowed ivory keys. I'm not much of a pianist, certainly not to Ruth's standard, but Mother had insisted I learn an instrument, and now my fingers move over the keys of their own accord, picking out first the melody, then the accompanying chords, of Beethoven's immortal Moonlight Sonata, a piece I had first learnt to please my parents, and then had learned to love myself. I play it through twice; no Ruth. Anxious now, I begin another piece, this one a simple minuet by Mozart, wondering all the while, where is she, and what could possibly be keeping her?