He turned to Savage. “ Did Nicholas have a torch with him?”

“Yes. A small one in his jeans pocket.” He was not really interested, but waited patiently while George thought, tried to work out the solution to the puzzle. He found none and shook his head.

“Did you find the jar? That held the chloroform?”

“No. That side of the building is right by the water. I reckon he threw it out of the window and into the tide. We’ll find it washed up in a couple of days. There were no fingerprints on the window frame or the catch, but if the window was already open, he wouldn’t have needed to touch it.”

George did not pursue the matter.

“Would you mind telling me what is in the preliminary forensic report?”

“They’ve identified some fibres found on the bench seat of the seawatching hide and on Charles Todd’s clothing. It’s a navy-blue material, a rough felt. It came, they say, from a duffel coat or a donkey jacket.”

“Yes,” George said. “ Yes. It would be.”

“You know where it came from?”

“Oh yes. There’s a duffel coat out there in the hall. It doesn’t belong to anyone. It must have been left behind and it’s used as a spare. The murderer was bound to use it, because it wouldn’t identify him. It’s very big and shapeless—from the back it would be hard to tell who was wearing it. It would act as a disguise.”

He hesitated, remembering the tapes he had heard the night before, the conversation between Savage and Nicholas Mardle about the arson at the Wendy House.

“Didn’t Nick mention to you that he noticed that the duffel coat was wet, when he came back after ringing waders on the night of the fire at Charlie’s house?”

“Yes,” Savage said, impressed by George’s memory, and by Nick’s apparent duplicity. “ He’s not daft, is he? He must have set fire to the house when he pretended to come back here. He probably wore the coat then, too. The timing would be right. He knew that we’d find traces of the coat in the hide, so he mentioned it first. He’s too clever by half.”

George ignored him. He was writing in his field notebook. When he finished he looked up. “Any fingerprints in the hide?”

Savage shook his head. He had given enough information. Now he needed George’s help. He had not invited Palmer-Jones to join him simply to spare his feelings.

“Would there have been chloroform on the premises?” he asked. “And if so, where would it have been kept?”

“There may have been,” George replied. “The observatory is used regularly by local schools in term time as a field centre. They use this room as a lab. I suppose it could have been used by the biologists in their experiments. But John would know.“

“Of course. I’ll have to ask him. Is this room never locked?” It was an accusation of carelessness.

“No,” George said. “ There’s never before been any need to lock it.”