Bruno Pontecorvo is an outstanding Italian and Soviet physicist. His life is amazing: he was born in Pisa, graduated from the University of Rome, worked together with Enrico Fermi and Joliot-Curie. During World War II he emigrated to the United States, where he worked for an oil company and invented the neutron oil logging method. Pontecorvo was involved in the English atomic project Tube Alloys and when he and his wife and three children suddenly emigrated to the USSR in 1950, suspicions of espionage were immediately aroused. Especially since for the next five years no one knew where Pontecorvo was or what he was doing. The book contains archival documents showing that all these years Pontecorvo was busy with research in the field of particle physics and had nothing to do with Soviet atomic spies or the creation of the atomic bomb in the USSR. Pontecorvo's remarkable ideas formed the basis of modern neutrino physics, and were the basis for today's extensive programme of research on neutrino physics. Six Nobel Prizes were awarded for experimental verification of Pontecorvo's ideas. This book is an account of his life and scientific discoveries.