At that hour Monsieur and Mademoiselle Stangerson, assisted by Daddy Jacques, were engaged in making an interesting chemical experiment in the part of the laboratory taken up by the furnaces.

Larsan says, unlikely as that may seem, that the murderer may have slipped behind them.

He has already got the examining magistrate to listen to him.

When one looks closely into it, the reasoning is absurd, seeing that the 'intimate'-- if there is one--must have known that the professor would shortly leave the pavilion, and that the 'friend' had only to put off operating till after the professor's departure.

Why should he have risked crossing the laboratory while the professor was in it?
And then, when he had got into The Yellow Room?
"There are many points to be cleared up before Larsan's theory can be admitted.