The Unexpected Guest is a novelisation by Charles Osborne of the 1958 play of the same name by crime fiction writer Agatha Christie and was first published in the UK by HarperCollins on September 6, 1999, and on October 1, 1999 in the US by St. Martin's Press.
The book was written following the successful publication of the novelisation of the 1930 play Black Coffee in the previous year. Like that book, the novelisation is a straightforward transfer of the stage lines and directions of Christie's script into a written narrative. Osborne chose not to add characters, lines or scenes which would alter in any substantial way what had been presented on the stage forty-one years earlier although minor amendments were made to produce suitable chapter endings.
The following year, Spider's Web underwent a similar novelization process, again by Osborne.
On a foggy night, a man called Michael Starkwedder breaks down near an isolated house and, entering it, finds the body of a dead man slumped in a chair. A woman stands over the corpse, gun in hand, and confesses to the murder but it is clear that she is covering up for someone else.