The Long Saturday Night by Charles Williams -- pdf

  Charles Williams was an American writer of hardboiled crime fiction. He is regarded by critics as one of the finest suspense novelists of the 1950s and 1960s. His 1951 debut, the pulp paperback novel Hill Girl, sold over a million copies. A dozen of his books have been adapted for the screen, most popularly Dead Calm.
--Wikipedia

  In The Long Saturday Night, the police wrongly think that John Warren killed his wife's lover. Realizing that all the circumstantial evidence points to him, Warren goes on the run, hoping to find the real killer. He probably wouldn't have succeeded but for the help of his astute and clever secretary.