The seven-sided tower-room was entered and searched. Through the uncurtained windows Paul saw the last sad light over by the western horizon reveal a grey, bleak landscape, icily forbidding, though surely no colder than the atmosphere of this room. Paul noted how Bourne hunched his shoulders against the chill, how Fletcher drew in long, shivering breaths. As quickly as they could, they finished with it and left, shutting the door behind them.

They met up with the other group in the corridor, just opposite the big glass dome set in the snow-covered roof. All the rooms on that floor had been searched and sealed. They were all empty. Almost certainly servants’ quarters in the house’s Victorian past, these dingy cramped rooms held trunks, bare iron bedsteads, cheap chests of drawers, and a large assortment of the other flotsam that every old house accumulates. Cumbersome vases and jugs, a row of heavy faded glass-framed photographs – was Arthur Howard among them, or the unlucky Mrs Howard? Paul wondered. There was even an old rocking-horse, its harness tattered, its paint worn away by the loving hands and knees of long-dead children.

And that was all.

In the narrow corridor they looked at each other. For a long moment no one spoke.

‘Right,’ said Pollard, ‘let’s get back down to the lounge. Mr Wilson, you and I will take a turn round the house outside if you don’t mind, and look at the cars. Mr Fletcher, Ted. You too. You go in the opposite direction. After we’ve checked the cars. Dr Bourne, Mr Hunt. You let us out and stay by the front door until we knock to get in again. Okay?’

In the sharp chill outside the snow was deep and powdery underfoot, almost blue-white in the torchlight. They swept snow from the car door-locks and made sure no one was inside the vehicles. As on that morning the cars were almost shapeless again under their white covering.

If there had been footprints, fresh snow must have obliterated them. The only marks on the surface when they returned to the front door were their own new-made trails.

In the hall, Paul watched Bourne re-lock the door. The ritual of threads stuck over the jamb by blobs of red sealing-wax was enacted with Bourne and Pollard pressing their signet rings into the soft wax.

It was agreed that Fletcher and Smith would restore the dining-­room to order while the three women prepared the evening meal. On Pollard’s suggestion the others retired to the lounge to discuss the situation. In the big room Hunt threw another log on the fire before sitting down opposite Paul. The other four men disposed themselves in the semicircle of armchairs and sofas.

Pollard ran a hand through his red hair.

‘I want to speak bluntly. What are we sure of?