“What happened?” said Bill, coming back.

“Just what you would expect. The sunlight came, and the shadow moved back again⁠—all in one movement.”

“And what happened yesterday?”

“The sunlight stayed there; and then the shadow came very slowly back, and there was no noise of the door being shut.”

Bill looked at him with startled eyes.

“By Jove! You mean that Cayley closed the door afterwards as an afterthought⁠—and very quietly⁠—so that you couldn’t hear?”

Antony nodded.

“Yes. That explains why I was surprised afterwards when I went into the room to find the door open behind me. You know how those doors with springs on them close?”