“That is perfectly true,” the Professor intervened.  “Mr. Quest called for us, as arranged previously, at ten minutes to twelve.”

The inspector nodded.

“I shall have to ask you to excuse me for a moment,” he said, “while I ring up Number 10 signal tower.  If Mr. Quest’s story receives corroboration, the matter is at an end.  Where shall I find a telephone?”

“In every room in the house,” Quest answered shortly.  “There is one outside in the passage.”

The Inspector left the room almost immediately.  The Professor crossed to Quest’s side.  A kindly smile parted his lips.

“My dear Mr. Quest,” he exclaimed, “our friend the Inspector’s head has been turned a little, beyond doubt, by these horrible happenings!  Permit me to assure you, for one, that I look upon his insinuations as absurd.”

[Illustration:  “Mr. Quest, your alibi has been found with A bullet in his brain.  I must put you under arrest.”]

[Illustration:  When Quest goes to the safe to produce the jewels, he finds them missing.]

“The man has gone off his head!” Laura declared angrily.

“It will be all right directly he comes back,” Lenora whispered, laying her hand upon Quest’s arm.

“If only some one would give me my jewels and let me go!” Mrs. Rheinholdt moaned.

The door opened and the Inspector reappeared.  He was looking graver than ever.

“Quest,” he announced, “your alibi is useless—­in fact a little worse than useless.  The operator at Number 10 has been found murdered at the back of his tower!”

Quest started.

“I ought not to have left him to those thugs,” he murmured regretfully.

“There is no automobile of yours in the vicinity,” the Inspector continued, “nor any news of it.  I think it will be as well now, Quest, for this matter to take its obvious course.  Will you, first of all, hand over her jewels to Mrs. Rheinholdt?”

Quest drew the keys of the safe from his pocket, crossed the room and swung open the safe door.  For a moment afterwards he stood transfixed.  His arm, half outstretched, remained motionless.  Then he turned slowly around.

“The jewels have been stolen,” he announced with unnatural calm.

Mrs. Rheinholdt pushed her way forward, wringing her hands.

“Stolen again?” she said.  “Mr. Quest!  Inspector!”

“They were there,” Quest declared, “when I left the house this morning.  It seems probable,” he added, “that the same person who is responsible for this double tragedy has also taken the jewels.”

The Inspector laid his hand heavily upon Quest’s shoulder.

“It does seem as though that might be so,” he assented grimly.  “You will kindly consider yourself under arrest, Quest.  Ladies and gentlemen, will you clear the room now, if you please?  The ambulance I telephoned for is outside.”