Quest suddenly whispered to the Professor.  Then he turned to the keeper.

“Bring him upstairs, Middleton, for a moment,” he directed.  “Follow us, please.”

The Professor gripped Quest’s arm as they ascended the stairs.

“What is this?” he asked hoarsely.  “What is it you wish to do?”

“It’s just an idea of my own,” Quest replied.  “I rather believe in that sort of thing.  I want to confront him with the result of his crime.”

The Professor stopped short.  His eyes were half-closed.

“It is too horrible!” he muttered.

“Nothing could be too horrible for an inhuman being like this,” Quest answered tersely.  “I want to see whether he’ll commit himself.”

They passed into the bedchamber.  Quest signed to the keeper to bring Craig to the side of the four-poster.  Then he drew down the sheet.

“Is that your work?” he asked sternly.

Craig, up till then, had spoken no word.  He had shambled to the bedside, a broken, yet in a sense, a stolid figure.  The sight of the dead man, however, seemed to galvanise him into sudden and awful vitality.  He threw up his arms.  His eyes were horrible as they glared at those small black marks.  His lips moved, helplessly at first.  Then at last he spoke.

“Strangled!” he cried.  “One more!”

“That is your work,” the criminologist said firmly.

Craig collapsed.  He would have fallen bodily to the ground if Middleton’s grip had not kept him up.  Quest bent over him.  It was clear that he had fainted.  They led him from the room.

“We’d better lock him up until the police arrive,” Quest suggested.  “I suppose there is a safe place somewhere?”

The Professor awoke from his stupor.

“Let me show you,” he begged.  “I know the way.  We’ve a subterranean hiding-place which no criminal on this earth could escape from.”

They led him down to the back part of the house, a miserable, dejected procession.  Holding candles over their heads, they descended two sets of winding stone steps, passed along a gloomy corridor till they came to a heavy oak door, which Moreton, the butler, who carried the keys, opened with some difficulty.  It led into a dry cellar which had the appearance of a prison cell.  There was a single bench set against the wall.  Quest looked around quickly.

“This place has been used before now, in the old days, for malefactors,” the Professor remarked.  “He’ll be safe there.  Craig,” he added, his voice trembling, “Craig—­I—­I can’t speak to you.  How could you!”

There was no answer.  Craig’s face was buried in his hands.  They left him there and turned the key.

2.

Quest stood, frowning, upon the pavement, gazing at the obviously empty house.  He looked once more at the slip of paper which Lenora had given him.  There was no possibility of any mistake:—­

    “Mrs. Willet,
    157 Elsmere Road,
    Hampstead.”