It was obvious his arrival had been spotted, because an officer approached as soon as McNab stepped out of the vehicle, introducing himself as the DS Jones who’d made the morning phone call. They shook hands and Jones said, ‘If you want a look inside, there are suits in the van.’

‘Any sign of Mrs Johnston?’ McNab asked as he kitted up.

‘None. We’ve done a house-to-house in the vicinity and are currently scouring open land up to and including Castle Hill, although that’s a bit of a problem.’

‘How so?’

‘I take it you’ve never walked in the woods that surround the castle?’

‘You guess right.’

‘Heavy undergrowth, jumbles of huge fallen rocks, really steep and rough ground. Almost impenetrable in parts.’

Glancing across, McNab could imagine what he was talking about.

‘Police dogs?’ he said.

DS Jones nodded. ‘Even they can’t get to some of the steeper spots.’

Dressed now, McNab indicated he was ready to go inside. The front door lay open, but he chose instead to walk the path taken by Pirie. Metal treads had been laid throughout, the SOCO team still moving around the interior. The local police were obviously treating this as a probable crime scene, rather than a straightforward disappearance.

When he entered the scullery, McNab could see why. Something had happened here, whether accidental or otherwise. McNab tried to imagine a scenario that fitted the blood spill.

He’d once caught his hand in the front door as a child, the snib practically removing the tip of his left forefinger. His mother had pressed it down, bound his hand up and taken him to A&E, where they’d swiftly sewn it back on.

When they’d returned home, the young McNab had been pretty impressed by the bloody mess he’d made. The place had definitely looked like a crime scene.

In this case, the abandoned knife in the sink could be the culprit. Whatever had happened here hadn’t been carried through to the kitchen, where two SOCOs were still at work. McNab introduced himself, took a good look round, in particular at the dressed chair Pirie had mentioned, then went to check out the remainder of the house.

First came the sitting room, surprisingly cold after the warmth of the kitchen, and obviously abandoned. The hearth had some ash in it, plus scattered soot on the fireplace and nearby carpet. McNab took a closer look and found the markings of birds in the sooty deposits. It looked like Karen had had an intruder . . . one of the winged variety.

He saved the bedroom until last. The door was open and from the doorway he could see the stuffed pyjamas lying on one side of the bed, the duvet on the floor where Magnus had pulled it off.

The reality was even more powerful than he’d imagined. Karen Marshall, as Magnus had indicated, was most likely not of sound mind. The Prof’s concern that she may have been trying to harm herself was beginning to look more likely. Add in the blood in the scullery . . .