The book is aimed at two kinds of readers: those who have some knowledge of mathematics, and those who have no knowledge of mathematics! It is a work of fiction based on actual incidents, and its heroes are real people who left their mark on the history of mathematics. It takes place in Paris in 1900 and is the story of a murder for which the greatest mathematicians of all time are considered suspects. Each suspect’s statement to the police leads to a mathematical problem. The first category of readers can try to solve the problems and determine whether or not each suspect has a valid alibi (a knowledge of secondary-school mathematics should suffice), whereas the second can simply skip this step. Either way, all readers will be able to follow the story. The project on which the book is based took third prize in the 6th Microsoft European Innovative Teachers Forum in Vienna in 2009. The distinction was awarded in the special category in which European teachers vote for the best projects.