The Urgent Hangman

Callaghan was five feet ten and thin. He had sevenpence halfpenny and a heavy smoker's cough. His arms were a little too long for his height and his face was surprising.
Slim Callaghan had been hired by beautiful Cynthis Meraulton to stop her cousins getting her step-father's money. But when the old man is murdered, the only suspect with no alibi and a giant motive is Cynthis.
Slim always played his cases the way they came, but it turned out the Meraulton job had more twists than a hangman's rope.
The Urgent Hangman was originally published in 1938.