“And I want you all to stay calm. There is absolutely no evidence that the killer is targeting police officers. But the obvious question to answer is, Did Adam stumble across something that could lead us to the individual who is behind these multiple killings?”

The knot in Wildeve’s stomach tightened. She was his wife. Why didn’t she know this?

“As you’ll be aware, we’ve carried out postmortems on each of the victims. Three have died from cardiac arrest and two from respiratory distress. Traces of vomit in some cases. Clearly, it’s more complicated than that. These were individuals, of course. With varying degrees of health. It would seem”—he cleared his throat again—“that the eyes were removed after death. But Mathilda Hudson, the pathologist, is confident that she has now identified what caused loss of life.

“What she—and we—have not been able to do—and what we must do as a matter of extreme urgency—is to discover what triggered the cardiac arrests, the respiratory failure. Why did they die in this way? And—”

A detective constable seconded from the homicide team in neighboring Brentwood interrupted Mac. He was loud, overconfident, speaking over the DCI. Wildeve did not know him, but she disliked him.

“What about gassing, guv?”

Adam. Struggling for breath. Enough time to know he was dying. She blinked, dug her nails into her palms. Found herself back in her past.

A flat. A broken window. A Do Not Enter note pinned to the bedroom door. As a younger officer, she had spent time with the Met’s dedicated chemical unit in London. “Carbon monoxide suicide,” the DC had explained when they’d forced their way in. The poor bastard had used a gas canister and was still wearing his mask.

Because his mouth and nose had been covered, there was none of the telltale smell of death. He had looked alive, healthy, almost radiant, the hemoglobin absorbing the carbon monoxide and pinking his skin. Was it possible that Adam had died this way?

“None that we can determine so far,” said Mac. “Two of the victims had dangerously low oxygen levels in their blood, as you’d expect with respiratory failure. But the pathologist could find no traces of gases that might have killed them.”

“But it’s true that a postmortem can’t pick up everything, right?” A senior female officer—Antonia Storm—had spoken with calm authority. “I mean, isn’t it impossible to identify some poisons, for example?”

An awkward quiet settled onto the room. Everyone knew that Storm had been working with the Met five years ago when notorious serial killer Brian Howley had ambushed and almost killed her and another officer with a banned pesticide. Old-timer DI Alastair Thornberry had persuaded her to transfer permanently to Essex. A long time ago, but her history still cast a shadow.