FOUR – Sherlock Holmes

"Don't let the fact that it's Boyd totally blind you," Eve advises quietly as they walk towards the concrete steps that lead down to the CCU's unprepossessing squad room. Grace raises her eyebrows a fraction, wondering about the implication. Eve shrugs in response. "Look, I know you've known each other for a long time and I know you're… very fond… of him, but if this was any other investigation…"

Instantly defensive, Grace shakes her head. "If Grant was really convinced it was an open-and-shut case there's no way Boyd would've been released on police bail."

"He hasn't been released without charge, though, has he? There's a big difference, Grace."

The grim truth, naturally enough, stings. As does Eve's acute perception. But how can she be expected to remain completely professional and objective about a murder case when the chief suspect is one of her closest friends? Grace glares at nothing in particular. "I'm aware of that, thank you. I'm just saying there's still room for reasonable doubt."

"I don't think he killed Erin any more than you do," Eve replies candidly, "but you have to admit that the evidence is compelling."

"There's got to be another explanation, Eve."

Their conversation is abruptly terminated as they finally enter the squad room for their first encounter with the unit's new temporary commander, Chief Superintendent William Marshall. To Grace's surprise he is dressed in full police uniform – immaculately pressed. A slim, wiry-looking man very similar in age to Boyd, he seems to exude an air of quietly self-important authority. Very short iron-grey hair, chilly blue eyes and the kind of narrow, intense features that remind her forcibly of an inquisitive and irritable bird of prey. He's not exactly unprepossessing, but there's nothing immediately likeable about him. Then, she is heavily biased – rather more than anyone else on the team, she suspects. It's not in her nature to pre-judge people, so she offers a tentative smile of greeting. She's not sure if Marshall notices – he certainly doesn't smile back.

He greets them coolly and civilly, and once everyone is expectantly settled he takes position in front of the recently-cleaned evidence board and opens with, "I'm not a detective and I'm not here to tell you how to do your jobs. I'm here to provide the authority and seniority you need to get those jobs done smoothly and efficiently. I do, however, expect to be kept informed of your activities. DI Jordan will act as a direct liaison between us and he will provide me with daily status reports." He looks at each of them in turn, his gaze unyielding. "I will be acting as this unit's commanding officer until the current… situation… is resolved – at which point either DSI Boyd will be returned to duty or a permanent replacement commander will be appointed. Until that time I expect you all to carry out your duties diligently, punctually and cooperatively." A tiny and rather meaningful pause precedes, "Doctors Lockhart and Foley, as civilian staff you will obviously be expected to continue to maintain the highest standards in your respective disciplines and to continue to collaborate fully with the rest of the investigative team."

Grace can feel the tangible ripples of uneasy tension that are coursing through the room. Collectively and individually they are not used to being addressed in such a pompously officious manner. It's certainly not the Peter Boyd way. It strikes her that Marshall might not have been the best choice of interim commander. Then again, perhaps someone at New Scotland Yard has an agenda. Make the most of the unexpected opportunity to bring the recalcitrant misfits of the CCU firmly back into line without having to risk the infamous wrath of their fiery commander. There's an air of expectancy in the room, Grace realises, as if her colleagues are waiting for her to issue a challenge by right of seniority. So be it. Carefully, she says, "With all due respect, Chief Superintendent, we are an extremely experienced multi-disciplinary team with a long and proven track record. I think we all know what is expected of us."

Marshall looks straight at her and although his expression is dispassionate and largely unreadable, she instantly forms the very strong impression that he has been forewarned, that someone has told him exactly where to look for any early signs of rebellion. His reply is quiet but steely. "I wasn't trying to imply anything else, Doctor Foley. But I think we are all well-aware of the particular difficulties that may arise due to the current unusual circumstances. This would seem to be an ideal moment to remind everyone that becoming in any way involved with Camden CID's investigation into the death of Erin Jackson is not the remit of either the CCU or its personnel."

Unintimidated, Grace coolly stares back at him. "Meaning?"

"Loyalty is to be commended," he says, "but it can sometimes be misplaced. DI Jordan, a word."

Grace watches in silence as the two men withdraw into Boyd's office. Next to her, Eve says dryly, "Well, that certainly told us, didn't it?"

-oOo-

Marshall's presence in Boyd's office feels wrong. As the day progresses it seems to Grace that he is not intending to have much interaction with anyone apart from Spencer. When encountered he is polite enough in a distinctly cool way, but he noticeably tries to keep his distance from the team and he doesn't attempt to directly involve himself in any of the daily round of discussions that characterise the way they usually work. Unlike Boyd, he does not suddenly and unexpectedly appear to ask awkward questions or offer unsolicited opinions, and he doesn't roam around apparently at random leaving flurries of chaos and confusion in his wake. He simply stays behind his borrowed desk, head firmly down over whatever it is he is doing. It's disconcerting to say the least, and in the unusual calm and quiet Grace finds it increasingly hard to concentrate. She does her best, steadily working through the contents of her in-tray, but the subdued atmosphere combined with her mounting worries about Boyd leave her tetchy and on edge.

Mid-afternoon she is interrupted by a diffident tap on her office door. She looks up cautiously. Stella. Smiling slightly in welcome she watches as the younger woman carefully closes the door behind her before advancing to say in a deliberately hushed tone, "They've got Boyd on CCTV heading north up Chalk Farm Road that morning. Spence just heard."

"Via a 'friend of a friend'?" Grace guesses.

Stella almost grins. Almost, but not quite. "Yeah, something like that."

"North up Chalk Farm Road, Stella? Do we know what time?"

"Seven forty-two."

"So he would have been on his way to meet me on Haverstock Hill?"

Stella nods. "Looks like it."

"Which exactly ties in with what he told me last night. After he left Erin's flat he went down to Camden Market and then back up to Regent's Canal."

"It's not much," Stella says quietly, "but it might help a bit."

Grace leans back in her chair, reviewing what she knows. "The flat is near Talacre Gardens. If Boyd had been coming to meet me straight from there, he'd have been heading due west on the Prince of Wales Road, not northwards on Chalk Farm."

Stella nods solemnly. "That's exactly what Spence said."

-oOo-

It's not conclusive proof. That's what Grace keeps telling herself as she drives determinedly east. It's not conclusive proof or anything like it, but it certainly adds weight to Boyd's account of his movements. It also puts increased pressure on the established time-frame for that fateful morning, further narrowing the precious little time available for him to have killed Erin. It's something. Not much, as Stella said earlier, but it is something.

She knows he isn't guilty. She just knows. It's more than her personal knowledge of the man and his character, far more than her professional opinion as an offender profiler; more even than the stubborn fancy of the weak, wishful part of her that is – always has been – secretly rather more than merely fond of him. It's a profoundly visceral thing, an instinct that remains absolutely unshakable in the face of all evidence to the contrary.

Boyd's house is halfway down a quiet residential side street not far from Trafalgar Road. A solidly middle-class enclave close to the north-eastern tip of Greenwich Park, it's a street predominantly occupied by reasonably affluent professional families. The kind of street where on Sunday mornings nearly-new cars are proudly washed and polished and well-tended lawns are carefully mown. Boyd's big silver Audi is parked at a sharp, rebellious angle on his short gravel drive. Grace wonders how long it will be before it is quietly collected and returned to the Met's carpool and immediately chastises herself for the pessimistic thought. Leaving her own car out on the street, she approaches the house with a brisk sort of defiance. She doubts Boyd is being kept under surveillance, but if he is, well, so be it.

The man who opens the door to her is strangely unfamiliar. He is tousled and haggard and she's never seen him quite so casually dressed. It takes her a moment to reconcile his current unkempt appearance with the good-looking, well-groomed man she knows so well. He looks down at her lugubriously, and despite everything there's a distinct trace of wry amusement in the way he pointedly says, "Yes? Can I help you?"

Realising that she's staring and that she must look more than slightly bemused, Grace recovers herself by saying tartly, "Oh, you really shouldn't have gone to the trouble of dressing up for the occasion, Boyd."

He shrugs, his shoulders not appearing quite so imposingly wide without the benefit of expensive tailoring. "I'm trying to adjust to the idea of spending the rest of my life wearing prison denims."

She feels her expression harden. "It's not going to come to that."

"No? Funny, I thought I was looking at fifteen years, minimum. Come in."

Grace follows him through the hall and into the big living room. She's visited the house on many occasions over the years, but never in such difficult circumstances. Accepting his offer of a drink, she seats herself on the sofa and says, "I take it you've heard all about our temporary commander?"

"Marshall? Yeah. God alone knows what the DAC was thinking, putting him in charge. The man's a complete…" Boyd grimaces. "Well, anyway. I think the last time he did any actual policing was about twenty years ago."

"He's told Spencer that he expects to see him wearing a suit and tie tomorrow."

Boyd hands her a glass. "And you all thought I was a royal pain in the arse."

The banter that usually flows so easily between them is forced, a brittle sort of façade that doesn't even begin to disguise the underlying strain and apprehension. Grace watches him settle into a chair, aware that he is deliberately keeping an abnormally wide physical distance between them – but whether for his sake or hers she isn't sure. It hurts, perhaps because it forcibly reminds her of the brutal nature of the crimes he is suspected of committing. Murder. Rape. It's appalling, all of it. She hears herself say, "We're doing everything we possibly can to help, Boyd, believe me."

He nods solemnly. "I know. And I'm more grateful than you'll ever realise, but…"

"Yes?"

"I hate to say it, Grace, but I don't think it's going to be enough."

That hurts, too. Because he sounds so weary, so fatalistic, and because a part of her suspects he might very well be right. With more conviction than she really feels, Grace says, "We'll make a break-through sooner or later, Boyd – we always do, don't we? But… there's something I need to ask you."

"Go on."

"It's… delicate." Understatement. It's not a question she wants to ask him and she's equally sure she doesn't really want to hear the answer he gives. If he deigns to answer at all.

Boyd snorts. "As you so helpfully pointed out yesterday, given the marvels of modern-day science it's a bit fucking late for me to be coy, isn't it?"

She can't ask him. Not directly. Turning the awkward question into a simple statement of fact might be easier. Grace avoids looking at him as she says, "One piece of tangible rather than circumstantial evidence Grant does have is that Erin scratched you. Your DNA was found under her fingernails, and when he examined you after your arrest the Forensic Medical Examiner found fresh scratch-marks on your chest and shoulders."

Silence. She risks a quick glance up to find that Boyd is giving her the kind of inscrutable look that suggests he thinks she's being deliberately and unnecessarily naïve. He shakes his head. "Jesus. What do you expect me to say? She was having a bloody good time, Grace. We both were. Do you want me to be any cruder than that?"

She really doesn't. It's not easy, but Grace manages to suppress the surge of embarrassment that threatens to tinge her cheeks and also to simultaneously ignore the sharp ignoble stab of jealously that really couldn't be more inappropriate under the circumstances. It's none of her business what he does, who he does it with or how he does it. But her imagination is a restless, traitorous thing and it busily works against her, conjuring tormenting images that she struggles to banish. Too sharply she says, "The alternative explanation, of course, is that she was fighting for her life."

The dark gaze settles bitterly on her. "I'm pretty damned sure she would have left me with more than a couple of faint scratches if that had been the case. Aren't you?"

Grace sighs heavily, unhappily. "I'm just trying to look at it from an impartial investigator's perspective. According to the forensics, one of two men killed Erin. One of them has been proved beyond any reasonable doubt to have been somewhere else at the time, the other was unquestionably in her flat that morning, had definitely had sex with her and was visibly scratched by her. Who would you have arrested if you were Grant?"

Boyd stands up abruptly and starts to pace, the tension in his body easily visible. "Fundamental principles. 'When you have eliminated the impossible, whatever remains, however improbable, must be the truth'."

"For God's sake, Boyd, this is not a good time to be quoting Sherlock Holmes."

"It's apposite," he growls. "I know I didn't kill her – which from my perspective therefore just leaves the improbable."

Grace nods, grudgingly accepting the logic. "All right. So?"

Boyd stops pacing and gazes intently at her. "Improbability, Grace. Given the evidence, it's apparently improbable that Fuller killed her, but is it actually impossible?"

-oOo-