"There will be ten teacups at number 4, Berwick Terrace, W. 8, on Wednesday, July 31, at 5 p.m. precisely. The presence of the Metropolitan Police is respectfully requested." 

Writing as Carter Dickson, the master of the locked room mystery John Dickson Carr returns to the Crime Classics series, pitching his series amateur detective Henry Merrivale against a seemingly watertight mystery: after the police are sent a note warning them about a forthcoming crime, a man is shot in a room on the top floor of a Kensington townhouse – a house watched from all sides during the murder. Surely nobody could have gotten in or out? And yet the man is dead, and just like the last time the police received a note like this, there are ten teacups set out at the scene of the crime. H.M. is drawn to unravel this bizarre crime, as the mysterious significance of the ten teacups in murders past and present pushes the police to their limits.