“It came to me quite suddenly. Something triggered Adam to action. When I realized what that was, the whole thing became obvious. But still I had no proof and I hadn’t been able to talk to Peter and Rob to eliminate them. The only witness was Terry Biddle and he had disappeared. All I could do was to make sure that it did not happen again, and I did try to keep Adam with me, but then Terry Biddle came back. His landlady, Mrs. Black, wanted to see me urgently, so I had to leave Adam with Molly.” He looked apologetically at Sally. “Of course, if I’d known what would happen …”

Sally smiled. George Palmer-Jones took his wife’s hand and said very softly, just to her: “You’ve talked to Adam. Do you mind telling them what happened?”

“Birdwatching was the only thing that Adam was good at,” Molly said. “It was the only thing that mattered to him. The day of Tom’s death he had gone to Rushy convinced that he was going to find a rare bird, something so rare that it would make him famous. But when he went into the field, Tom French had already found the rarity.”

“Tom French found the bimaculated lark?” Rob asked.

George interrupted: “ That was the trigger, you see. Once I linked Tom French to the bimaculated lark, Adam had to be the murderer.”

Molly continued: “Tom must have seen the bird almost as soon as he left the hotel building, and he followed it to the edge of the park, where you all saw it later in the day. Adam found him there, watching it. Adam believed implicitly that he was meant to find the bird, and that Tom French had in some way tricked or betrayed him by getting there first.

“If Tom had let him play a part in it, had consulted him about the bird and shared it with him, perhaps Adam would never have lost control. It’s impossible to say, irrelevant even. Adam was very disturbed and would have broken down some time. But Tom irritated Adam. He lectured to him about the lark. He talked to Adam as if he were a child, as if he knew nothing about birds. Adam says that he did not mean to kill Tom when he hit him. He lost his temper. Tom would not stop talking.”

“So Tom French found the bimaculated lark,” Rob repeated. He was very impressed, almost envious. He turned to George:

“You see, it’s like I said. ‘ Once a twitcher, always a twitcher.’ He wasn’t played out after all.”

There was a silence. It was a tribute to Tom’s ability as a birder.

George continued his explanation.

“Because of the way the body was lying, we knew that Tom hadn’t been killed where he was found. We couldn’t decide how the murderer carried the body to the pool. It’s about three-quarters of a mile from the White Lodge, too far for one person to carry a dead weight. But Adam was seen with the body by one person. That person was Terry Biddle who works in the White Lodge, in the kitchens. He’s a little mentally defective, but it seemed that his evidence was reliable. He knew Tom. Terry told us that he had seen someone with Tom’s body going up the marsh track, but then Terry ran away before he could give us any details.