Chief Superintendent Littlejohn, of Scotland Yard, on holiday in Provence, finds himself involved in the case of a tour from which the English coach-driver and the conductor have disappeared. The body of the conductor is found shot through the head near the pleasant little town of Sospel among the high mountains and dangerous roads behind Nice.

When he learns that his conductor has been murdered and that he is suspected, Bennion, the driver, fearful of the methods of the French police, which he has read about in thrillers, gives himself up personally to Littlejohn, explaining that he is running away from his wife.

The confusion caused by keeping the touring party under control, making hazardous journeys among the hairpin bends of the Alpes Maritimes, chasing a gang, which is obviously in mischief, and acting as interpreter for those tourists who do not know French, keeps Littlejohn busy for quite a while before he and his friend Dorange of the Nice Sureté sort out the whole affair.