Marshall caught his breath. “Coincidence,” he said flatly. “I’m on my way to see him now.”

“Oh. Then he did get in touch with you himself?”

“Not with me,” said Marshall. “With the Stripper.”

“God rest his soul . . .” Sister Ursula murmured.

“So. I’m on my way now. If you could meet me there and bring his letter—”

“Lieutenant, I know our order is a singularly liberal one, but still I doubt if Reverend Mother—”

“You’re a material witness,” Marshall said authoritatively. “I’ll send a car for you. And don’t forget the letter.” Sister Ursula hung up and sighed. She had liked Professor Flecker, both for his scholarly wit and for his quiet kindliness. He was the only man who could hold his agnostic own with Father Pearson in disputatious sophistry, and he was also the man who had helped keep the Order’s soup-kitchen open at the depth of the depression.

She took up her breviary and began to read the office for the dead while she waited for the car.

“It is obvious,” Professor Lowe enunciated, “that the Stripper is one of the three of us.”

Hugo Ellis said, “Speak for yourself.” His voice cracked a little, and he seemed even younger than he looked.

Professor de’Cassis said nothing. His huge hunchback body crouched in the corner and he mourned his friend.

“So?” said Lieutenant Marshall. “Go on, Professor.”

“It was by pure chance,” Professor Lowe continued, his lean face alight with logical satisfaction, “that the back door was latched last night. We have been leaving it unfastened for Mrs. Carey since she lost her key; but Flecker must have forgotten that fact and inadvertently reverted to habit. Ingress by the front door was impossible, since it was not only secured by a spring lock but also bolted from within. None of the windows shows any sign of external tampering. The murderer presumably counted upon the back door to make plausible the entrance of an intruder; but Flecker had accidentally secured it, and that accident,” he concluded impressively, “will strap the Tripper.”

Hugo Ellis laughed, and then looked ashamed of himself.

Marshall laughed too. “Setting aside the Spoonerism, Professor, your statement of the conditions is flawless. This house was locked tight as a drum. Yes, the Stripper is one of the three of you.” It wasn’t amusing when Marshall said it.

Professor de’Cassis raised his despondent head. “But why?” His voice was guttural. “Why?”

Hugo Ellis said, “Why? With a madman?”

Professor Lowe lifted one finger as though emphasizing a point in a lecture. “Ah, but is this a madman’s crime? There is the point. When the Stripper kills a stranger, yes, he is mad. When he kills a man with whom he lives . . . may he not be applying the technique of his madness to the purpose of his sanity?”