When Le Directeur suggests Le Guide's food inspector Monsieur Pamplemousse take a brief jaunt to sample the gastronomy of Rome, Pamplemousse knows the offer is too good to be true. But when the only string attached seems to be that on the return journey he escourt the Director's schoolgirl niece Caterina from her Rome convent school to her uncle's Paris home, Monsieur Pamplemousse begins to relax. Until, that is, he sees the schoolgirl in question ... and spots her every-present shadow, an Al Capone-lookalike whose hostility Pamplemousse senses even across a crowded restaurant car.
However, it is when the Rome-Paris Express pulls into Gare de Lyon and his charge apparently disappears into thin air that Pamplemousse really begins to worry. Especially when he discovers the lustrous Caterina is the daughter of one of Sicily's most powerful mafiosi, a man who will not take the loss of his cherished daughter at all kindly...