About an hour later, I walk past Ruth's workstation on my way to the tech suite, and am surprised to see that her monitor is off, her machine powered down, the desktop clear of all its usual clutter of mugs and dossiers, reports and empty biscuit packets. Zaf, who now occupies the desk opposite hers, flicks me a look over the top of his screens. "Hiya, if you're looking for Ruth, she's gone." My consternation must be evident, because the younger man quickly adds, "Not gone-gone. You know, she's just left for the day." I gawk at him, my mind racing off on a dozen different tangents. The staff cafeteria isn't even serving lunch yet, so why would Ruth have gone off like that, without a word? I glance towards Harry's office, where I had seen her headed earlier, a pile of files under one arm. Right, so let's find out, then, I tell myself briskly, let's march in there, beard the lion in his den and find out what he's done with Ruth. Easy…

It's not. Twice I start towards the inner sanctum, and twice I find myself elsewhere. Once in the men's room, diametrically opposite Harry's office, and once in the service corridor beyond it. I don't like having to ask for information; if Harry wants someone to know the details of an operation, generally they do, and it goes against the grain to question him about something he could have easily told me, if he was so minded. But in the end, I simply have to know, and so once more I set out across the Grid, my heart pounding and my chest growing tighter with each step. Knocking discreetly on the heavy wooden sliding door to his office, I wait for Harry's "Yes, Malcolm?" before pushing it open.

Confused as to how he could have concluded that it was me, I blurt, "How did you know who it was?" before I can stop myself. Harry regards me with a long, steady look, one with humour hidden in it, beneath his piercing gaze. "Do you really have to ask? You're the only member of the team who would even bother to knock, in the first place. And there's only Zaf, Colin, you, and me here at present. Colin has never so much as set foot in my office… or not to my knowledge," Harry adds, reading my face like a book, "And as I can see Zaf industriously beavering away out there, by simple deduction, when you have eliminated the impossible…" Together we finish the famous detective's cardinal precept, "Whatever remains, however improbable, must be the truth!" Harry gives me one of his rare, real smiles, and indicates a chair. "Ah, Malcolm, I always knew you'd be a Baker Street Irregular too." Sitting down, I smile back, forcing myself to remain nonchalant and devil-may-care, or as nonchalant as I ever manage to be. This is not the FSB, nor the CIA, or any other of half-a-hundred acronyms for fear, I remind myself; this is the internal security ministry of Her Majesty's government, and Harry Pearce is not only my boss, but my friend of nearly fifteen years. Just ask the question, Wynn-Jones!

"So, to what do I owe the pleasure?" Harry prompts, after I have sat silently for a few moments. "Oh, erm, Zaf happened to mention that Ruth has left for the day, and I was a bit worried about her. It's very unlike her to leave so early, so I just, um, wanted to check everything was all right?" Harry's dark hazel eyes scrutinise me minutely, but for once I manage to hold his gaze without blushing. "I should have known you'd notice. You don't miss a trick, do you, Malcolm." His voice is neutral, but there is a tightening around his eyes, a sudden stillness to him, that makes me very nervous indeed. I blunder on, "It's just that if…if she's unwell, or anything like that, she really should have reported it to me, I am the first aid officer for the Section, after all, and it's my duty to record any incident that affects someone's ability to do their job, or anyone who is taken ill unexpectedly…" Harry relaxes visibly, and holds up a hand, stopping me mid-sentence. "You're quite right, and I'm sorry if Ruth's rather precipitate departure has caused you any concern. She's perfectly safe, even if at this moment she is well on her way to being slowly bored to death." My eyebrows shoot up at this peculiar assertion, and Harry grins. "I've sent her back to GCHQ." It seems as if the room has suddenly lurched to one side, or turned topsy-turvy: What? Did he really just say that Ruth's gone back to Cheltenham? What are we going to do now? WHY? Why would he send the best analyst he's ever had…oh. Oh, no. No. Surely he wouldn't just send her away…not now. Not if…

"Whatever you're thinking, it's definitely uncomplimentary." Harry's voice is drier than a sun-bleached skeleton in the Sahara, and about as cuddly. I colour hotly, embarrassed once more by my complete inability to school my features into an immobile, unreadable mask, as everyone else here seems able to do at will. "Sorry, but did you just say Ruth has been transferred back to GCHQ?" My voice sounds steadier than I feel, for which I am grateful. Harry winks at me, to my utter amazement, and then begins to laugh, while I look at him uncomprehendingly, and wonder if I am in fact still asleep on the Chesterfield at home, and am simply having a bad dream. Heaving for breath, Harry finally manages to regain enough control for normal speech.

"Your face, just now…it was a picture of perplexity! Ruth's not been transferred, Malcolm, she's been sent. As in, on an op. I need someone on the inside there, someone whom Adam can introduce as a sympathetic contact to the bully-boys he's dealing with, and she's the perfect officer for the job. She knows what passes for culture at Cheltenham inside out, but she's loyal to us. And she's been agitating, lately, to be allowed to do more field work…she's back to her old self, it seems." After Danny's death, are his unspoken words, but I hear them anyway. After I have spent countless hours listening to her as she worked through her grief and guilt, supporting and loving her, I think, but do not say. As if she's a bit of kit, damaged in the field, that I have carefully restored and repaired, and is now ready for him to use again, as he sees fit…

I don't know what to think, or how to feel: has Harry really just said that he's putting Ruth back into the field, this time against a violent and dangerous lot of would-be fascists, and that sending her back to the hated job at GCHQ is all part of it? And that Ruth has been actively campaigning for field work? Harry knows she's not field trained…something's off, here. Why would he risk it, risk her, especially if she's…unless, that is, he doesn't know? "Malcolm, are you all right?" Harry's voice breaks into the maelstrom whirling inside my head, and I realise I haven't spoken since I first sat down. "I'm fine, thank you. Just a little…taken aback, I suppose, that I wasn't briefed about this earlier, especially if I'm to do night duty…" I hate having to interrogate Harry like this, but my uneasiness is expanding exponentially, and I need his reassurance that we are not about to be plunged into darkness, each of us left to grope blindly without any knowledge of the others are doing, while Harry watches like some omnipotent deity. My hands are trembling ever so slightly at my temerity, so I fold them, one holding the other, in my lap. Harry's keen eyes miss nothing. "Perhaps you should see the MO," he suggests, "you really don't look well." I ignore this, and fix my eyes on his, waiting for his reply. He sighs, and gets up, crossing to the drinks cabinet behind his desk. He pours himself four fingers of whisky, holding up the decanter enquiringly over a second tumbler, but I shake my head; if I start drinking spirits now, I'll be muddle-headed for the rest of the day, for I very rarely imbibe anything stronger than red wine, and certainly never on duty.

Harry gives me a "suit yourself" shrug, splashes a drop of spring water into his drink (as if that will make the slightest bit of difference…) and goes on to fill the other glass, handing it to me with a wry little smile. "Never drink alone, isn't that what they say? Your health!" We chink glasses, two friends of long standing saluting each other…or two rivals, sizing each other up? Stop it, I berate myself, this is Harry, for heaven's sake, not a villain out of a bad melodrama; Harry, whom I have known and admired and obeyed unhesitatingly for over a decade. Harry drains his glass to the dregs in one long swallow, before pouring a refill as I sip my water. His capacity for strong drink is legendary in the Service, first cultivated during his stint in Northern Ireland, and subsequently during his time in Germany, and then at various points behind the Iron Curtain, but I can't help but wonder why he is having recourse to it now, especially as the sun's not even over the yardarm…

"Malcolm, I'm going to be frank with you." I quickly set my glass down to avoid spilling the contents, and clasp my hands tightly together. "I think Ruth has great potential, beyond that of an analyst. She can think on her feet, she speaks several languages, she's very good at gaining people's confidence…and she wants to be more than just a desk spook, she's told me so herself." I blink in horror. Ruth, regularly in the field? Dear God… I realise he is waiting for me to speak, so I gather my thoughts and protest, "But Harry, she's not a trained field officer! She's not physically fit, for one thing, and she hasn't done advanced weapons handling or self defence…her counter surveillance skills are only basic…and she's such an asset here! Field staff can be recruited out of the universities and the armed services easily enough, but to put Ruth in harm's way…she doesn't have the killer instinct, Harry, you know she doesn't. Ruth would want to negotiate with an attacker, not shoot them before they can kill her first."

Harry hears me out, his face impassive. "I value your opinion, Malcolm, but I have to say I think you're wrong on this. Perhaps we should be thinking more about cross-pollination within the Section, developing the staff in areas beyond their current duties; it would make us more responsive, more adaptable, and more resilient to attrition." I can't quite believe my ears, and yet in Harry's words, I can detect the echo of Ruth's; her intellectual DNA is instantly recognisable to me, who knows how she thinks. So this is how she has sold it to him, this mad idea of hers… but why? Why on earth would she want this? That is a conundrum I cannot answer, not yet, but I can certainly answer Harry; taking my courage in both hands, I prepare to disagree. "I can't agree with you there, I'm afraid. I think that the best model is the current one, with highly trained staff carrying out specialised duties, but you're the boss. And at least GCHQ is a safe place for her to be."

I keep my voice steady, as if we were discussing a hypothetical scenario in the briefing room, working through the possibilities until consensus is reached as to the best course of action, drawing on all my experience to try to appear as detached and logical as possible. Harry nods in acknowledgment that GCHQ is indeed a safe place for her to be (or so I most fervently hope), and I take a deep breath. "I still don't quite see why I shouldn't have been briefed about this prior to Ruth leaving for GCHQ, though. Is there some sort of difficulty of which I am not aware?" Apart from the bloody enormous difficulty I currently find myself in, that is… Harry's face closes as if shutters have been put up, and my blood runs cold. I know that look all too well. It's the look he wears when he goes to Whitehall, his 'ask me no questions and I'll tell you no lies' look. "All you need to know is that it suits my purposes to have someone on the inside at GCHQ, at present, and I trust you will keep that little tidbit to yourself. Now, hadn't you better go and see what young Zaf is up to? Nothing too… cool, I hope." And I am dismissed, my friend resuming the mantle of boss spook in an instant.

After my interview with Harry, it is a positive relief to get back to my desk and do something normal, something familiar, something like monitoring Zaf's online activities. He has hacked into Sampson's online shopping account with Waitrose, and is gleefully substituting various groceries in the latest order for other, less useful items. Out with the Persil laundry powder, in with…Oh no, no, not a gross of Durex condoms, Zaf, one has to be more subtle than that…fortunately, he seems to think so too, for a few seconds later, the one hundred and forty-four boxes of prophylactics are removed in favour of two fresh lobsters. Then he changes the delivery time, so that the groceries will sit on Sampson's doorstep all day. My nose wrinkles at the thought; even in September, it doesn't take long for seafood to go off, and lobster is notorious for spoiling fast.

Next, deodorant is exchanged for fly spray; oh, well done, Zaf, now you're getting it! As a finishing touch, he removes replacement razor blades from the order, and substitutes a Brazilian waxing kit instead, whatever that may be. I can't help but smile as I think of Sampson's outrage when he arrives home to discover that merry hell has been played with his weekly shop, and that reminds me to ensure that when he rings the Waitrose customer service centre to complain, as he undoubtedly will, that the call is diverted here instead. I quite enjoy playing the role of the obstructionist call centre worker, remaining imperturbable as the voice on the other end grows ever more shrill... I have had a lifetime of experience, after all, in dealing with Mother, and it stands me in good stead at times like these. Besides, there's always the Mute button, a feature sadly lacking when conducting conversations in the flesh.

I watch in fascination as Zaf efficiently breaks into the Thames Water mainframe next – he's really quite good – and submits an urgent work order for the mains water to be turned off to Sampson's house for the next three days, citing "pipe replacement" as the reason. After that, he seems to feel he has done enough for the moment, and returns to more mundane tasks, such as emailing three young, pretty, female members of the administration staff with an invitation to join him (each at different times, of course) for drinks… Rolling my eyes, I log out of his user profile, after leaving flags to notify me when he next begins to hack an external system. It is possible to know too much about one's colleagues, and I have no wish to invade Zaf's privacy…it is also possible, it seems, to know far less about the woman I love, than I would ever have suspected...

Before I can pursue that deeply disturbing line of thought, Colin returns from lunch, and we chat about the tasks ahead of us. He wants to fix Adam's computer while he is off the Grid, and I agree; he has already ordered a new phone for Fiona, but in the meantime she is using one from the props pool, a glitzy gold Nokia that fits with her PR consultant image. I explain that I have drawn night duty, and he looks sympathetic, but unsurprised. "I thought you might, seeing how short-staffed we still are. Do you want me to stay back with you for a bit? I don't mind, and I could do a bit of server maintenance while it's quiet." I thank him for the offer, but I am sure that he must have something better planned for tonight, and say so. He looks up sharply, and I realise my innocent comment has somehow struck a nerve. "We're not all as lucky as you," he snaps, and I stare at him in surprise, trying to work out what I've done. "You really don't remember, do you? You've been so wrapped up in yourself and your precious…"

"Shhh!" I urge him, seeing Zaf approaching. "Hey, Colin, Malcolm, I'm off out for a bit. Got some pamphlets to deliver," he tells us with a wide grin, showing us what he has worked up. I wince as I read the cover: attacking people with disability is a very bold move for Sampson to make in today's society, but at my look of doubt, Zaf explains that Adam has called to advise him about some of the more repugnant (and as yet unpublished) policies of the British Way. "No smoke without fire, yeah?" and with that, he heads for the pods, car keys already in hand. He's a young man in a hurry, all right…and then I remember why Colin is cross, and remorse floods through me.

Colin had been seeing someone until quite recently, a girl he had met online while playing an MMOG, and had subsequently struck up an acquaintance with, after discovering she lived in London too. According to Colin, their friendship was on the verge of blossoming into something rather more intimate, when the Shining Dawn attack had occurred. Colin's young lady had been at Camden Markets that day, and while she had fortunately not been seriously injured, she had refused to leave her house since, or to see anyone outside her immediate family. PTSD is the diagnosis, and after several attempts to contact her, both in person and online, had been met with paranoid suspicion, if not downright hysteria, Colin reluctantly came to the conclusion that he would be better to move on, and leave her to her healing. Apparently, she had been devastated that he had been unable to rush to her side when she texted him from University College Hospital's A &E department after the bombing, and then he had been at a loss to explain why he hadn't contacted her for more than a week, as she had not yet been vetted; the S24 form was on Harry's desk at the time, awaiting his signature, buried amongst other, more pressing paperwork.

Colin has been filling me in about all this during the last fortnight that I was at work, and now I recall how upset he had been, although at the time I had been completely focused on Ruth, trapped behind the icy walls of her grief. Colin had thought that this girl…Linda…Lily…Lucy!, that was her name, could have been The One. After the first few meetings, he had hardly been able to contain his enthusiasm, telling me about her over lunch at the Cricketers, his face lighting up as he spoke. "She's a geek like me, she works as a programmer for BT, she'd rather spend an evening together gaming or watching a DVD, than going out clubbing, she's smart, we have the same sense of humour, and she loves sci fi too…Trek, Galactica, Who, and she's even introduced me to a few new shows; have you ever seen Firefly?"

At the time, my own thoughts had preoccupied me, and I had barely been able to take in the deluge of details about Lucy, beginning with the first flush of excitement and discovery, and ending in despair, as Colin realised that she too was a casualty of the Camden bombing, psychologically if not fatally, and that she was slipping away from him. But I vividly remember, now, Colin retrieving the socialisation form from Harry's desk a couple of weeks ago, and shredding it, stony-faced… I have been a selfish friend, so caught up in my own feelings for Ruth that I have failed to see what Colin has been going through, and yet he has shown me nothing but consideration and kindness in return. I feel terrible, the heat of shame burning through me as I realise how carelessly I have treated my friend of six years, in favour of a woman I have known for barely two.

Behind his screens, Colin is simmering at my thoughtless "Shhh!"… I had better make amends, and fast; like me, Colin is slow to anger, but possessed of a formidable temper if provoked far enough. I walk around to his side, and he rolls his chair back abruptly and stands up to leave, eyes hard. I sidestep, blocking his path to prevent him from storming off, and offer my hand, saying, "You're quite right, I've been colossally selfish over the last few months, and there's no excuse for my thoughtless behaviour. I should have been a better friend, and I want you to know how truly sorry I am about Lucy. She sounded lovely…"Colin looks at me, then down at my hand, then back at me. "You've been a complete ass, lately, just so you know," he informs me brusquely, before adding, "But then, Ruth would be enough to do anyone's head in…"

Colin still hasn't taken the hand I am holding out for him to shake, and I am not quite sure what I should do with it. Taking off his spectacles, he pinches the bridge of his nose for a moment, closing his eyes as if trying to erase his memories, and sighs, "She was. Lovely. Lucy, that is…" his voice softer than usual, and when he looks at me, his eyes are glistening. "I thought I'd finally found her, you know? It was early days, but it just felt right. And then…" My heart turns over as one of Harry's favourite sayings comes to mind, 'And there, but for the grace of God, go I…' Aloud, I say, "I know, and I'm so sorry, Colin." He notices I am still proffering my hand, and shakes his head, before he seizes it and pulls me into an awkward hug, much to my astonishment. "Us geeks have to stick together, right?" he says, releasing me, and I step back, not sure whether I'm coming or going; the last man I hugged was my father, the morning that I left home to go up to Cambridge. Colin sees my discomfiture and gives me a toothy grin. "That was for having your head stuck so far up your…"I frown; I don't like vulgarity, and Colin knows it. He stops, and changing tack, offers to make tea. "It's what we Brits are meant to do after any sort of emotional display, isn't it?" he observes, collecting our mugs and heading through to the tea room.

I slump into my chair, covering my face with my hands as I seek to shut out the world momentarily. People are exhausting, but I wouldn't have them any other way; messy and emotional and irrational and illogical and full of contradictions, true; and also capable of heart-stopping passion, love in all its forms, unwavering loyalty and friendship that outlasts the ages…we're all just human, in the end. So very human… I vow to do better at remembering this, in future. As for the hug, it's hardly the norm for men of my age, granted, but Colin, on the other hand, is Generation X through and through, and with that lot, anything is possible. I decide to overlook it.

The rest of the day passes uneventfully, and by seven-thirty I am alone on the Grid. Even Harry has gone off, muttering something about getting back to Scarlett before she bonds completely with the next door neighbours, and refuses to accompany him home. Apparently, this had happened with the dog before her. Harry, who commands absolute loyalty at work, had been tried and found wanting in this area by a small brown dog, and thus had been abandoned for a more reliable master. There would be something deeply ironic about this anecdote, if it weren't so terribly sad…

As I am compiling the day's static obs reports on Sampson – he had indeed rung through to complain loudly about "the effing state of his effing shopping", and I had taken a perverse delight in answering him softly in Welsh, until he had rung off in a rage, making all sorts of improbable threats against Waitrose in general and me in particular, I hear quick, light footsteps approaching the tech suite, which I have taken over as my base of operations for the evening. To my surprise, Fiona appears, sleekly beautiful in the suit she has worn to meet with Sampson as 'Emily Glover'. She hesitates for a moment before approaching me in the dimly lit room, to ask if I have heard anything from Adam, yet. The underlying anxiety in her voice tugs at my heart; I understand exactly how she feels, for I too have someone I love out in the field.

I reply truthfully in the negative, and when her face falls, I feel compelled to reassure her. She has already turned to go, so I speak her name gently. "Fiona?" She pivots around, as graceful as a dancer, eyes wide with enquiry. "He'll be all right, you know," I say encouragingly, and she smiles appreciatively, "Thanks, Malcolm, for everything. Will you be OK tonight?" I nod, and tell her that I'll let her know as soon as I hear from Adam. A look of relief passes across her face, and then she is gone, her high heels clicking rapidly towards the pods, and I am left alone, with only my thoughts and my fears for Ruth for company, amid the myriad tiny hums and clicks that make up the nocturnal symphony of the Grid; just technology and me, keeping watch. Standing on the wall, as Ruth would say.

Usually, I don't mind night duty, welcoming the chance to catch up on some of the maintenance and upgrade tasks that can only be performed during downtime, and the silence suits my solitary nature. But after the last week of intense connection and interaction with Ruth, I feel as lonely as a ghost tonight, my heart aching at her absence already, and not just because of the way things were left between us. I miss her terribly, and for once, there is no solace to be found in the familiar sounds and surroundings of the Grid. An overpowering urge to get out of this artificial world, even if just for a moment, comes over me, so I transfer all comms to my mobile phone, and head up to the roof. As soon as I emerge out of the stairwell, wheezing slightly as the fresh, cold air fills my lungs, I see the moon, huge and golden, hanging over the river. I recall last night, when it appeared to be a baleful eye, watching my distress; tonight, I pray that its light will find Ruth, and shine on her, too. After a few minutes, my phone rings: Adam. He gives his call sign and the correct message to indicate he is all right, and I make the appropriate response. Only Ruth to check in, now; remembering my promise to Fiona, and finding the damp chill rising off the Thames more than I had bargained for without my overcoat, I head back downstairs. All around me, it seems that the city itself is a living, breathing thing, freed by the darkness to dream its ancient dreams, and somehow, I no longer feel so alone. I have faith in nights…

Fiona almost cries with relief when she hears my voice, telling her Adam is safe – it is her first night alone since Danny was killed - and just before midnight, my own apprehension is assuaged when Ruth checks in. She gives her call sign and message, and trapped by my extensively documented insistence that field staff follow the correct procedures and not engage in idle chit-chat, I can say nothing more than the scripted reply, but I close my eyes and listen to her breathe for a moment before she rings off. I hope that she is doing the same thing, wherever she happens to be; and that for her, I exist as completely in that strangely intimate space between talking and breathing, as she does for me. Sighing, I turn my attention back to the field reports coming in from Adam and Aunty May, one of our best housekeepers, but now that I have heard from Ruth, the loneliness has receded somewhat, and I resolve to keep my own counsel and jump to no conclusions, until I can speak to her face to face. To help me stay alert, I put on a CD from the small stash I keep in my desk – Rachmaninoff's All-Night Vigil – and the magnificent, heart-swelling sound of Russian liturgical music, sung by one of the best choirs in that vast and tragic land, fills the dimly lit room.

The Grid and I hum on together, watching over the city, all through the night.

A/N: On the rooftop, Malcolm is remembering a line from the poem You, Darkness, by Rainer Maria Rilke. And the famous detective, he of the cardinal precept that Harry and Malcolm quote, is of course Sir Arthur Conan Doyle's immortal creation, Sherlock Holmes.

A MMOG is a Massively Multiplayer Online Game. Colin likes them. Malcolm, not so much.