An inverted detective story, occasionally known as a "reverse whodunnit" or "howcatchem", is a crime fiction structure in which the commission of the crime is shown or described at the beginning, usually including the identity of the perpetrator. The story then describes the detective's attempt to solve the mystery. There may also be subsidiary puzzles, such as why the crime was committed, which are explained or resolved during the story.

This format is the opposite of the more typical "whodunit", in which all of the details of the perpetrator of the crime are not revealed until the story's climax. The first such story was R. Austin Freeman's The Case of Oskar Brodski published in Pearson's Magazine in 1912. The television series Columbo is one of the best-known examples of this genre.

R. Austin Freeman described how he invented the inverted detective story in his 1912 collection of short stories The Singing Bone.

Some years ago I devised, as an experiment, an inverted detective story in two parts. The first part was a minute and detailed description of a crime, setting forth the antecedents, motives, and all attendant circumstances. The reader had seen the crime committed, knew all about the criminal, and was in possession of all the facts. It would have seemed that there was nothing left to tell. But I calculated that the reader would be so occupied with the crime that he would overlook the evidence. And so it turned out. The second part, which described the investigation of the crime, had to most readers the effect of new matter.

This was perhaps more common by the 1930s. Ngaio Marsh included a foreword on the subject in her 1935 novel Enter a Murderer.

When I showed this manuscript to my friend, Chief Detective-Inspector Alleyn of the Criminal Investigation Department, he said:

"It's a perfectly good account of the Unicorn case, but isn't it usual in detective stories to conceal the identity of the criminal?"

I looked at him coldly.