The story opens with the narrator on his way home from the theatre one evening, when his attention is drawn to a crowd gathered around a road accident in the West End of London. A taxi has hit a pedestrian. Out of the crowd emerges Charles, an old friend, supporting a fainting women. They had been the passengers in the taxi, and Charles now charges the narrator with seeing the lady home.
This is the start of a highly eventful evening, in which the husband of the woman dies in a mysterious manner and the two of them agree to collude over the evidence to be given at the inquest. The most important thing, however, is to keep Charles's name out of it.