“What’s this?” he asked abruptly.  And he knocked nonchalantly on the door of the tank-room.

Audrey was acutely alarmed lest Jane Foley should respond, thinking the knock was that of a friend.  She saw how idiotic she had been not to warn Jane by means of loud conversation with the detective.

“That’s the tank-room,” she said loudly.  “I’m afraid it’s locked.”

“Oh!” murmured Mr. Hurley negligently, and he turned the searchlight of his gaze upon the three bedrooms, which he examined as carefully as he had examined anything in the house.  The failure to discover in any cupboard or corner even the shadow of a human being did not appear to discourage him in the slightest degree.  In the third bedroom—­that is to say, the one nearest the head of the stairs and farthest from the tank-room—­he suddenly beckoned to Audrey, who was standing in the doorway.  She went within the room and he pushed the door to, without, however, quite shutting it.

“Now about the tank-room, Miss Moze,” he began quietly.  “You say it’s locked?”

“Yes,” said the quaking Audrey.

“As a matter of form I’d better just look in.  Will you kindly let me have the key?”

“I can’t,” said Audrey.

“Why not?”

Audrey acquired tranquillity as she went on:  “It’s at Frinton.  Friends of mine there keep a punt on Mozewater, and I let them store the sail and things in the tank-room.  There’s plenty of room.  I give them the key because that’s more satisfactory.  The tank-room isn’t wanted at all, you see, while I’m away from home.”

“Who are these friends?”

“Mr. and Mrs. Spatt,” said Audrey at a venture.

“I see,” said the detective.

They came downstairs, and the detective made it known that he would re-visit the drawing-room.  Inspector Keeble followed them.  In that room Audrey remarked: 

“And now I hope you’re satisfied.”

Mr. Hurley merely said: 

“Will you please ring for Aguilar?”

Audrey complied.  But she had to ring three times before the gardener’s footsteps were heard on the uncarpeted stone floor of the hall.

“Aguilar,” Mr. Hurley demanded.  “Where is the key of the tank-room?”

Audrey sank into a chair, knowing profoundly that all was lost.

“It’s at Mrs. Spatt’s at Frinton,” replied Aguilar glibly.  “Mistress lets her have that room to store some boat-gear in.  I expected she’d ha’ been over before this to get it out.  But the yachting season seems to start later and later every year these times.”

Audrey gazed at the man as at a miracle-worker.

“Well, I think that’s all,” said Mr. Hurley.

“No, it isn’t,” Audrey corrected him.  “You’ve got all my keys in your pocket—­except one.”

When the police had gone Audrey said to Aguilar in the hall: 

“Aguilar, how on earth did you——­”

But she was in such a state of emotion at the realisation of dangers affronted and past that she could not finish.