Puzzled and worried, French began to believe that he was on the wrong track in London and that he must return to Devon and try once more to get the truth from Domlio. But he would not relax his watch on Mrs. Berlyn and Pyke. Pyke he would himself shadow next day, so that if he communicated with Berlyn he, French, would learn the latter’s whereabouts.

He turned into the nearest telephone booth, and ringing up the Yard, arranged for reliefs for himself and Sergeant Carter. Then, Sergeant Deane having taken over the watch in Kepple Street, he went home.

Next morning he called at the Yard for Carter, and about nine o’clock the two men reached Kepple Street.

“That’ll do, Deane. You may get away,” French greeted the night man. “Nothing stirred, I suppose?”

“Nothing, sir. No one in or out the whole night.”

“Now, Carter,” French went on, “it’s your show mostly to-day. Pyke knows me and I’ll have to keep in the background. You stay about here and I’ll get a taxi and wait round the corner. If I see your signal I’ll come along.”

Time soon began to drag for the watchers. Evidently their man was in no hurry. Ten o’clock came, then eleven, then eleven-thirty, and still he made no sign. French began to grow seriously uneasy.

At last he could stand it no longer. He got out of his taxi and strolled up to Carter.

“Go up to the door and ask for him, Carter. If he sees you say I sent you to ask if he would call round at the Yard any time this afternoon.”

Taking his subordinate’s place, he watched him walk up to the door and knock. In a moment the door was opened and Carter disappeared.