Somehow, somewhere, Stoner had made himself fully acquainted with Mallalieu and Cotherstone's secret.

Did Stoner's death arise out of a knowledge of that secret?
On the face of things there could be little doubt that it did.

Who, then, struck the blow which killed Stoner, or, if it did not actually kill him, caused his death by bringing about the fall which broke his neck?
Was it Mallalieu ?--or was it Cotherstone?
That one or other, or both, were guilty of Kitely's murder, and possibly of Stoner's, Brereton was by that time absolutely certain.

And realizing that certainty, he felt himself placed in a predicament which could not fail to be painful.

It was his duty, as counsel for an innocent man, to press to the full his inquiries into the conduct of men whom he believed to be guilty.