The Man at the Carlton by Edgar Wallace — Read

TIM had a problem to which no ready solution offered. His training and character made the acceptance of the woman's suggestion impossible. But here was the stark fact: Mary Grier was bigamously married to a man who was undoubtedly a murderer and as undoubtedly a dangerous maniac. He had seen the look in the young man's eyes and had instantly diagnosed his disorder aright.

So that was old Awkwright's secret, the explanation of those mysterious midnight trips which had followed the arrival of the drunken Martha at Clench House.