You will forgive me." He passed through the open French windows and neither of them made any further attempt to detain him.

Their silence was a little unnatural and from the walk outside he glanced for a moment behind him.

The two men were sitting in exactly the same positions, their faces were turned towards him, and their eyes seemed to be following his movements.

Yet there was a change.

The professor was no longer the absorbed, mildly benevolent man of science.