She zoomed in and tilted the camera screen towards him without thinking. He stepped in close to look and Kelly suddenly felt crowded, hot, trapped. Her fight or flight response tried to kick in. She had to stamp on it firmly before she either belted him or ran. Or both.

“So, the opposite of something like a comet tail?”

“Exactly. As the droplet hits a hard surface the back edge holds its form while the front edge breaks into what looks like a tail. It’s how we can fix the directionality of the spatter.”

Lytton straightened without apparently realising how near he’d been to serious injury. He was frowning.

“And you think there’s some problem with that directionality?”

“It’s possible.”

“Look just spit it out will you?”

Kelly took a breath and said in her best evidence-giving voice, “I observed an additional void pattern on the side of the bathtub in this area here.”

Lytton leaned over the bath holding his tie flat to his chest with one hand to prevent it dangling.

“I don’t see this void you’re talking about.”

“You won’t,” Kelly said. “It would appear to have been filled in.”

“Filled in.” Again that dead flat sceptical delivery. Again the command: “Show me.”

Kelly indicated with the pen. His face stayed expressionless.

“I can’t see any difference.”

“It appears correct at first glance but when you look closer you can see the directionality is actually totally opposite,” she allowed. “My guess would be someone dipped into the spilt blood and flicked it across the void to cover it. If it wasn’t for the difficulty of flicking it upwards instead of down I might not have spotted it.”

For maybe ten long seconds he said nothing. Then he stepped back as if to distance himself from her.

“That’s it?” he demanded. “That’s the reason you’ve put this whole job on hold? A tiny patch of blood sprayed so fine you can hardly make it out with the naked eye, when I’ve had half of Thames Valley and the Met crawling all over this place for days? And that’s all you have?”

His hands twitched in a gesture of frustration or despair. Kelly refused to cringe in the face of his anger. She kept her head up, aware she came barely to his chin.

“Once this is gone it’s gone,” she said indicating the bloodied bathtub. “I just need to be absolutely sure I’m doing the right thing.”

Lytton snorted. “Yeah of course you do.” He passed a tired hand across his face. “I . . . apologise. I’m sure you can appreciate that I’m anxious to get this over with—try to put it behind me.”

“Of course. Just as I’m sure you can appreciate that we have to work strictly by the book.”

He tensed, mouth flattening. For a moment she saw the swim of mixed emotions in his face, his eyes. Instead of the sorrow she’d been expecting there was only anger and confusion and a fleeting trace of something Kelly recognised as guilt.

Whatever else had been part of Veronica Lytton’s life she considered, that didn’t include a happy marriage.

She forced a smile to soften the blow and put a placating hand on his arm. “I’m very sorry for your loss Mr Lytton but I can’t ignore what the evidence is telling me.”

Lytton withdrew his arm fast, almost jerky as if he felt tainted by her touch. He was at the doorway before he delivered his Parthian shot with unknowing but deadly accuracy:

“This evidence you set such store by—suppose what it’s telling you is wrong?”

3

Matthew Lytton stood in the shadows by his open study window and stared down into the rear courtyard where the crime-scene cleaners’ van stood parked.

He could see the pair of them lounging in the front seats—doors open, waiting—and was aware of a ticking resentment at their idleness, however involuntary.

Lytton had made his considerable fortune in construction, demolition and renovation. Casual labour was a necessary evil that all too often lived up to its name. He’d become adept at turning up on site when his guys least expected. If he’d found any of them sitting on their backsides reading like this pair he’d have fired them so fast they would’ve left scorch marks.

Now, from his vantage point on the upper floor, he could see the big black kid was engrossed in a sports magazine. The woman was reading a book. Not a cheap paperback but a hardcover. When the distant trill of her cellphone drifted up to him she held her place with a bookmark rather than dog-ear the page before answering it.

As a man who’d grown up without books Lytton had come to treat them with respect. Grudgingly he found himself thinking better of her for doing the same.

When he first saw the woman striding along the corridor towards him with her choppy black hair and her pierced nose he’d thought she was just a girl. Something about the petite frame, the easy way she moved despite the unflattering garb, spoke of youthful vitality.

But where he’d expected truculence she’d responded only with reason. And when he looked deeper he saw she was nearer his own age than that of her young apprentice. That had thrown him as much as her stubborn refusal to be riled. Even if his overriding impression remained one of suppressed energy behind the calm facade.

His late unlamented wife had been the epitome of calm, cool and collected. He once swore that it was unnecessary to put ice in Veronica’s afternoon Pimm’s. One touch to her lips and the glass would be laced with it. But what you saw was what you got. The only fire that burned inside that perfectly stage-managed body was ambition. First for him and—when that was achieved without apparent satisfaction—for herself.

He glanced down and realised he was holding their wedding photograph. Slowly, he smoothed his thumbs across the ornate silver frame. He’d come across the picture while he was sorting through his wife’s things and been almost surprised she’d kept it.

Mind you she kept everything else. There seemed to be endless notes, shorthand reminders of conversations, social engagements, names and dates. Deciding what was rubbish and what was important had begun to give him a headache. And that was before he’d had his run-in with the cleaners.

Finding the photo gave him an excuse to pause a moment and reflect. It hadn’t been a big wedding but Veronica had still insisted on something overly lavish for their finances at the time. Looking at their frozen expressions with the benefit of twenty years’ hindsight he reflected that neither of them looked particularly ecstatic at the union.

He’d had no illusions he was the love of her life of course, just as she had not been his. They’d discussed their proposed marriage in coolly practical terms before the announcement was drafted for The Times.