Lord Darcy Investigates is a collection of short stories by Randall Garrett featuring his alternate history detective Lord Darcy. It was first published in paperback in 1981 by Ace Books. The book collects four Lord Darcy short stories originally published in the magazines Analog Science Fact & Fiction in October 1974 and December 1976, and June 1965, Fantastic in May 1976, Isaac Asimov's Science Fiction Magazine in April 1979. The Lord Darcy stories are set in an alternate world whose history supposedly diverged from our own during the reign of King Richard the Lionheart, in which King John never reigned and most of western Europe and the Americas are united in an Angevin Empire whose continental possessions were never lost by that king. In this world a magic-based technology has developed in place of the science of our own world.