Starting in 1967, Julian Symons wrote three books with title beginning "The Man Who..." The first two, certainly, rank among his finest work, and it's no coincidence that when the Detection Club marked his 80th birthday with a collection of short stories in his honour, it was called The Man Who.., and each story had a title containing that phrase. The three books were not a trilogy, and are entirely distinct from each other. There are no common characters, although a strong sense of irony, and a sharp sense of humour, are common features.
The Man Who Killed Himself was the first of the three novels, and it features meek, unhappily married Arthur Brownjohn, a character who closely resembles Dr Bickleigh in Francis Iles' Malice Aforethought. This is not the only parallel between the two stories, and I've no doubt that Symons was consciously trying to take elements from the work of Iles (whom he admired, as I do) and fashion them into a contemporary mystery. He does so with great success. This is quite a short book, but it's genuinely gripping.
Arthur is leading a double life. He finds an outlet for the more, shall we say, outgoing aspects of his character by creating Major Easonby Mellon, a dodgy chap who runs a very dodgy matrimonial bureau. Mellon is married to a nice but unintelligent woman whom he has persuaded that he is actually a secret agent. The early scenes are very funny, but then the plot thickens - and it becomes progressively darker. Arthur, like the other 'Men Who...' is essentially a weak man, whose personality flaws make him a potential murderer.
Ultimately, this book is a study of a man's psychological disintegration. Symons had tackled this subject before, notably in The 31st of February, his first significant crime novel, and he would revisit it subsequently, but never with such zest as in this book. The combination of a clever plot and ironic prose is a real delight. I recommend it unreservedly.