Murder Runs in the Family by Hulbert Footner

The completely reckless man is rarely taken. Towards morning a hangdog figure tapped on a window of Professor Sempill's laboratory in the rear of Mrs. Peake's house. Lance could never tell where he had spent the intervening hours. Recollection was lost in a fog of pain.

The windows were dark now, but Lance knew that the old man was a light sleeper. Sure enough, he presently appeared at the window, clad in the ancient dressing-gown that he frequently wore for days together. He was not at all surprised. He threw up the sash and Lance climbed over the sill.