Doctor Goodwood's Locum is a 1951 mystery detective novel by John Rhode, the pen name of the British writer Cecil Street.^[1] It is the fifty third in his long-running series of novels featuring Lancelot Priestley, a Golden Age armchair detective. It was published in America the same year by Dodd Mead under the alternative title The Affair of the Substitute Doctor.^[2]

In the market town of Patham, Doctor Greenwood takes his annual August holiday with his wife and hires a locum to take over the practice while he is away. But his replacement Stephen Thornhill goes missing after just a few days, and when a body is discovered Scotland Yard are called in to investigate with the assistance of Priestley.