In Paris, at an exhibition on the peaceful use of atomic energy, a preparation of radioactive cobalt was stolen… Suspicion falls on the lyceum students who were at the exhibition. Several students, independently of the police searching for the cobalt thief, along the way become acquainted with the use of atomic energy in production and in scientific research. The book, many of whose pages are written with humor, gives the reader the first information about the peaceful atom. The book is designed for a wide range of readers – high school students and adults.