A couple of hours later, I log off for the night, one of the last people on the Grid. Harry, as ever, is still working, with his phone pressed to his ear and an annoyed look on his face as he glares at his computer screen. Ruth is still at her desk, poring over the latest batch of satellite images, pausing occasionally to glance across at Harry's office. I pull on my coat and tell Ruth goodnight, not wishing to engage any further with her while Harry's about, but she doesn't look up, just nods in reply. I am about to go through the pods, when I sense someone standing behind me. Turning slightly, I see Harry, still in his shirtsleeves, face unreadable. "Walk with me a moment, will you?" he says in that unmistakable tone which brooks no argument, and leads the way off the Grid, towards the underground car park. He says nothing until we are in a blind spot in the car park – yes, they do exist, even in Thames House – and then he rounds on me. "What the bloody hell do you think you were doing, taking Ruth to that damn Requiem thing?" he growls, jaw set like an intractable bulldog's. Oh, hell's bells. He knows. Of course he knows, he's the great Harry Pearce, and what he doesn't know isn't worth knowing, where Section D's concerned…how much, exactly, does he know?

I stand stock still, reminding myself to breathe normally as I try to work out what's going on. Harry continues, in his most clipped tones, "It has also come to my attention that you signed out Registry files – on the weekend – and then took them to Ruth, at home." I blink, and then it hits me. Sam. Sam has been spying on Ruth. I can't believe that Harry has sanctioned this. Harry is glaring at me, now, and I realise he is waiting for an answer.

Willing myself not to blush from nervousness at being put on the spot, I reply, "Erm, well, this is a bit awkward. Ruth said she needed the files because she wanted to catch up on her static obs over the weekend. I didn't know what she wanted those particular records for, and it was only that I had mentioned that I was uploading some software upgrades on the Grid that she even knew to ask me if I would get them for her, and then it was such vile weather that Saturday, I was happy to save her the bus trip into Thames House…" a strange look passes across Harry's face when I mention the word bus, and I trail off. Oddly, some of his anger seems to have dissipated, and he sighs. "Ever the gentleman, aren't you, Malcolm? But that does not excuse your part in this…this balls-up with the Requiem. Ruth is not a field spook, nor are you, and this man, Foran, Forsythe…" "Fortescue," I supply –even though events appear to be going seriously pear-shaped, a tiny part of me is secretly amused at Harry's struggle with the name of the erstwhile object of Ruth's interest.

Harry is not laughing, however. "Whatever the bloody man's name is, he doesn't warrant this level of attention. He's a low-priority subject. What did she think she was doing?" Harry's glare is piercing, and I have an uncomfortable moment of insight into how it would feel to be interrogated by him. Drawing a deep breath to allay the tightness in my chest (damned if I'm going to use my inhaler in front of Harry – that would be a huge tell), I reply, looking him squarely in the eye. "I think she wanted to prove that she could do it – make contact, I mean, under a pretext, with a subject of interest. You know how much she wants to be a real spy, as she rather naively puts it. I went along to the Requiem to keep an eye on her, make sure she didn't get into any trouble. I thought you would rather someone was with her." Harry eyes me cynically, and then says, "I suppose you know she engineered some sort of lunch date with the man as well? Earlier in the week?"

I shake my head, thinking that little Scottish Sam has been most thorough in her betrayal of her co-workers. "Malcolm, after you picked up her attempt at sneaking secrets to GCHQ last year, I have kept a close eye on our Miss Evershed, and until now I have had no further reason to doubt her loyalty to the Service. But this…I can't ignore it, given her previous wobble. I'll have to have it out with her." There is something behind those words, and in his eyes, that makes me decide that I have had enough of this conversation. Quite frankly, I'm also feeling very uncomfortable that Harry has reminded me of the unwitting part I played in discovering Ruth's one and only, misguided attempt to be a GCHQ mole. I retrieve my keys from my coat pocket and walk away, out of the blind spot, muttering something about needing to get home to check on Mother. Harry nods and steps back, hands in his pockets, face shuttered. I am aware that Harry has chosen to let me go, while allowing me to maintain the illusion that I'm walking away from him off my own bat, as it were. I make my way to my car, and once safely ensconced in its familiar surrounds, I close my eyes and rest for a moment, breathing in the rich smell of old leather and polished wood. What a day. If this is what being more engaged with life is like, I almost miss my quiet, dull existence…almost. Harry's final words are still ringing in my ears… I'll have to have it out with her… I know he is referring to her perceived wobble in judgement, but quite suddenly, I find myself wishing he would have it out with her on other matters, too. Matters which affect me more than Harry could, or should, ever know.

I'm tired, so tired…my mind roams back over the day, and again I have the feeling that I'm missing something, somewhere. It is not a feeling I get very often, so I sift again through the day's events, looking for anything which might explain the sense of dread now churning in my gut. I shouldn't have fudged the Archive surveillance footage, of course, but nor did I want anyone to witness the conversation that took place between us. I relive it in my normally excellent memory, but with a more analytical than emotional focus this time. That odd little moment, when Ruth placed her hand over my heart…at the time I had been too caught up in visceral reactions to really think about it; but now it strikes me as distinctly strange, not like Ruth at all. In fact, Ruth has been not like herself all day… the coldness she had shown earlier, followed by the sea change in her behaviour in the Archive, and the haunted look in her eyes… The feeling that I am in a trap, which has yet to be sprung, returns. Again I try to recall each second of our encounter in the Archive, certain that the answer to what is bothering me lies there. And then I see it, or rather, feel it again – the slight change in the quality of Ruth's touch as her hand slipped away from my chest. Very carefully, I open the breast pocket of my shirt, and look inside, then reach across to the glove box and remove a pair of needle-nose tweezers and a tiny plastic ziplock bag. Using the tweezers, I reach into my pocket and delicately extract a minute slip of paper, and then I drop it into the bag and seal it.

Digging around a bit more in the glovebox, I find a magnifying lens which I sometimes use when working with our smaller bugs, and peer at the paper by the dim interior light of the Rover. On one side is printed the word, 'Gelert,' and on the reverse is a smear of what is almost certainly human blood. My own blood runs cold as I grasp the implications of Ruth's cryptic message. Every Welsh child knows the sad story of Gelert, the faithful hound of Prince Llewellyn the Great. I can still hear my father's soft voice, telling me the tale…

In the long ago and far away time, there lived in North Wales a Prince called Llewellyn, and he had a palace near Beddgelert. The Prince loved three things well, and one above all; his beautiful wife, his faithful hound, Gelert, and his infant son, who was the pride of Llewellyn's life. As a boy, the Prince had raised Gelert from a whelp, and the two were inseparable companions; wherever one was, there too was the other. Together they had hunted all the beasts of the forest; the black-hearted wolf, the cunning wild boar, and the great red deer, and each had many times saved the other from danger. Gelert was fierce in battle, yet as mild as milk with his master; and each was to the other devoted. Now, as is the way of these things, the Prince's lady was in time delivered of a fine, healthy son, and at once the Prince showed him to Gelert, and bid the hound guard him well.

Some weeks after the birth of his son, the wish to ride out hunting in the fine Autumn air came strongly upon the Prince, and whistling up his hounds and his horse, he set out; but Gelert was nowhere to be seen; and no search of the stables and kennels could discover him. The Prince had a fine day's hunting, and when he rode back into the stable-yard, the truant Gelert came bounding to greet him, full of joy, but with his fur bedabbled and stained with blood. A cold hand seized the Prince's heart, and in fear he went swiftly to find his son, Gelert hard upon his heels. Upon reaching the child's chamber, a fearful sight met the Prince's eyes; the child's cradle upturned and empty, and blood upon the floor and the bedclothes. With a great cry of anguish, the Prince drew his sword and straightway plunged it into Gelert's side, for the treacherous hound had slain his son. The hound screamed in sorrow as he died, and from the far corner of the room, there came in reply a child's cry. The Prince found his son unharmed, and on the floor beside him, the body of a great wolf that Gelert had killed, for his master had bid him guard his son. The Prince, filled with remorse at his deed, never smiled again…

Gelert, the faithful companion who was slain by his master for an imagined wrongdoing…and on the other side of the paper, Ruth's blood. Ruth's face looking up at me, tight with fear. Ruth, who is on her second strike with Harry, after last year's unfortunate and uncharacteristic lapse in judgement. "I'll have to have it out with her…"Shuddering, I remember the look on Harry's face as he let me go, and with hands that shake, I start the engine and drive off without even allowing it time to warm up properly, so discomfited am I. Ruth, Harry, and me… the Prince is easy – that's Harry, of course, the ruler of Section D. The only question now is who is the wolf, and who the hound?