They walked a short way in silence before Pritchard opened the third door on the left, entering an almost empty room with a large window on one side, a viewing gallery. Through the glass Hawkins saw what looked like an operating theatre, bathed in blue light. Two anti-contamination-suited operatives moved back and forth between various pieces of scientific equipment. On evenly spaced tables in the centre, three human shapes lay prostrate beneath plastic sheets, the nearest of which was folded down to reveal Joel Kowalski’s torso.

She turned to Pritchard. ‘What are we doing out here?’

‘Minimizing risk of contamination.’ He tapped the large monitor mounted on the wall to their left, waking it. ‘New facility, new practices, I’m afraid. No visitor access without full pre-screening, and you’re in a hurry. Frustrating, I know, but it does make a certain amount of sense. The fewer people who come into direct contact with a cadaver, the less time we spend discounting foreign DNA strands. And from this room we can watch forensic pathologists at work via high definition CCTV link.’ He reacted to her frown. ‘I understand your vexation, Detective, but in this instance it’s academic, because what I’m about to show you was destroyed during our investigation.’

He turned to face the monitor, tapping through various menus until the screen filled with thumbnail images. ‘The clues were quite well buried, so we didn’t detect them at first. That’s why I wanted you here. It’s something of a challenge to explain.’

Hawkins waited, studying the adjacent room, realizing that the workers inside weren’t using the equipment; but clearing it away.

‘OK, here we go.’ Pritchard dragged her attention back as he selected one of the photographs, a close-up of a partially dissected human organ. ‘This is Colin Wilson’s left atrium. As you know, two weeks’ worth of natural degradation made it very difficult to determine what killed him, or the other two. In fact, I had given up on traditional methods and switched to investigating their underlying physical conditions, looking for clues.’

He used a virtual tool to zoom in on the gory epicentre. ‘In that kind of search, the heart is a good place to begin, and here I made an interesting discovery.’ He waved at the fleshy mess. ‘Do you notice anything unusual?’

Hawkins snorted. ‘Looks like regular offal to me.’

‘Understandable, I suppose.’ Pritchard pointed at a darker area of tissue. ‘Do you see the discoloration?’

‘Yes.’

‘Excellent. It wasn’t visible pre-incision, but its rate of deterioration was also lessened as a result, thereby—’

Hawkins interjected. ‘I hate to rush you, Gerry, but frankly I’m just after the money shot.’