"There are other clues," he said, meditatively.
"In the diary?"
"Partly. 'For instance, why was Anthony so strong in the arms? He was rather puny when he became governor; nothing about him developed except his arms and shoulders. We know that…. Eh?"
"Yes, of course."
The doctor nodded his big head. "Then again, you saw that deeply worn groove in the stone railing of the balcony over there. Eh? It was about of a size to contain a man's thumb," added the doctor, examining his own thumb reflectively.
"You mean a secret mechanism?" asked Rampole.
"Again," said the doctor, "again — and this is important — why did he leave, behind him a key to the balcony door? Why the balcony door? If he left those instructions in the vault, all that his heirs would need to get at them would be three keys: one to the corridor door of this room, one to the vault, and one to the iron box inside the vault. Why, then, include that fourth key?"
"Well, clearly because his instructions entailed going out on the balcony," said Rampole. "That was what Sir Benjamin said when he was talking about a death-trap out there…. Look here, sir! By that groove the size of a man's thumb, do you mean a spring, a mechanism, to be pressed so that―"
"Oh, nonsense!" said the doctor. "I didn't say a man's thumb went there. A man's thumb, even in the course of thirty years, wouldn't have worn that groove. But I'll tell you what would have done it. A rope."
Rampole slid off the edge of the table. He glanced over at the balcony door, closed and sinister in the faint light of the candle.