"They weren't in the fire-proof vault?" asked Tarling, and Sir Felix shook his head.
"No," he said, "they were in a strong-room; and curiously enough, it was in that strong room where the fire originated. The room itself was not fire-proof, and it would have been precious little use if it had been, as the fire started inside. The first news we received was when a clerk, going down to the basement, saw flames leaping out between the steel bars which constitute the door of No. 4 vault."
Tarling nodded.
"I need not ask you whether the books which Mr. Milburgh brought this morning had been placed in that safe, Sir Felix," he said, and the knight looked surprised.
"Of course not. They were placed there whilst you were in the office," he said. "Why do you ask?"
"Because in my judgment those books were not books at all in the usually understood sense. Unless I am at fault, the parcel contained three big ledgers glued together, the contents being hollowed out and that hollow filled with thermite, a clockwork detonator, or the necessary electric apparatus to start a spark at a given moment."
The accountant stared at him.
"You're joking," he said, but Tarling shook his head.
"I was never more serious in my life."
"But who would commit such an infernal act as that? Why, one of my clerks was nearly burnt to death!"