A festive atmosphere envelops the line of people waiting for one of the last showings of a popular London musical comedy. Excitement is so big, and crowd is so large that people are being carried rather than walking. As the line eventually reaches the box office one man drops on his knees and slowly spreads on the floor. People jump to help, thinking he had fainted, but get horrified when they see a knife stuck in his back. There are so many witnesses, but nobody saw anything and nobody can tell when it happened as the man has been held upright for a while, carried by the moving crowd. Inspector Alan Grant of Scotland Yard is summoned to investigate the case. Known for his wit and guile Inspector Grant will have to deal with a lot of false leads and clues, which will take him all the way to Scotland, in order to solve this mysterious murder case.