“True. We haven’t any proof whatsoever that he came back, although we know that his accomplice did, supposing our theory to be true. Well, there it is, Frant. We can only waste time discussing it further, until we get some fresh facts, which may or may not fit into the theory. Now about that question we were discussing this morning, I think I shall get on to the Sussex police and see if they can help us.”

At that moment the house telephone rang. The inspector answered it. “Send him up,” he said into the instrument.

“The Chief Constable of Dover,” he said to Frant. “Now what on earth can he have to tell us?”

The head of the Dover police was an old friend of Mallett, who had collaborated with him more than once before. The inspector knew him for a capable, businesslike officer who was not likely to waste his time on trivialities. He came briskly into the room, shook hands with Mallett, nodded to the sergeant and came to business at once.

“Had to come up to see the Commissioner this afternoon,” he said briefly, “and thought I might as well bring this with me. Safer than the post, anyway.”

He put a sealed packet into Mallett’s hands. Mallett opened it and drew out a limp, discoloured blue booklet. He examined it in silence, his eyebrows raised in astonishment. Then he uttered a long whistle.

“Where on earth did you get this?” he asked.

“Fisherman brought it in this morning. Found it just below high-water mark a hundred yards or so east of the harbour last night. Tide sets that way, y’know. Got his statement for what it’s worth”—he pulled a folded sheet of official paper from his pocket—“but nothing in it beyond that. May have been in the water days, a week perhaps, impossible to say. High tides all this week and a sou’-westerly gale to help ’em along.”

“I’m very much obliged to you,” said the inspector. “This may be really valuable. You’ll stay for a cup of tea, won’t you?”

The Chief Constable shook his head. “Got to be getting along,” he said. “Hope it’ll help you a bit. You’ve got a sticky job, I’m afraid. So long.”

As the door closed behind him, Mallett tossed the object in his hand to the impatient Frant.

“Exhibit No. 1!” he exclaimed. “What do you think of it?”

Frant looked at it. “A passport?” he said. Then, opening its discoloured cover: “Colin James’s passport!”

“No less,” said the inspector. “The identical one that our friend of this morning had stolen from him three months ago. It’s in pretty bad order, but the name is still legible, thank goodness. Now just turn to page seven.”

Frant did so.

“The pages have stuck together,” he observed, “and the inside here is quite unspoilt by the water.”