The Crooked Hinge by John Dickson Carr

"And do you think I like what I am doing?" asked Dr. Fell.  "Do you think I like one word I've said or one move I've had to make?  Everything I've told you about the woman and her private witch-cult and her relations with Farnleigh was true.  Everything.  She inspired the murderer and directed the murder.  The only difference is that she did not kill her husband.  She did not make the automaton work and she was not the person in the garden."

John Dickson Carr, The Crooked Hinge, Penzler Publishers (originally published in 1938)

Kudos to Otto Penzler for publishing The Crooked Hinge, part of his estimable publishing effort to bring back out-of-print mysteries.  John Dickson Carr, an American who lived mostly in England, published seventy-five novels between 1930 and his death in 1977.  Many of these novels are "impossible" or "locked room" mysteries which strain plausibility, something that adds to one's pleasure reading them today.  Unfortunately most of Carr's work remains out-of-print currently, never having the readership of Agatha Cristie or other contemporaries, possibly because his "detectives," such as Gideon Fell, didn't interest Carr as much as the details of the puzzles and the personalities involved.  The Crooked Hinge is wonderfully detailed and complex, proceeding from an incident during the sinking of the Titantic to an imposter posing as Sir John Fairleigh and an automaton two hundred years old.