Ivor was supposed--according to Girard, the detective--to have tried in vain to escape by way of this high balcony, on hearing sounds outside the door while busy in searching the dead man's room.

Girard said that he had seen him first, by the light of a bull's-eye lantern, which he--Girard--carried, standing at bay in the open window.

There was a photograph of this window, taken from outside.
There was the balcony: and there was the balcony of another window with another balcony just like it, on the adjoining house.

I looked at the picture, and judged that there would not be more than two feet of distance between the railings of those two balconies.
"That would be my way to get there--if I can get there at all," I said to myself.

But there was hardly any "if" left in my mind now.