The focus of this film is on Canada's nuclear research centre at Chalk River, Ontario. Key to atomic progress are the radioactive isotopes. The insertion and handling of these isotopes in the deadly interior of the reactor are shown in detail. Also shown are the applications of radioactive isotopes in various fields of endeavor, particularly medicine, agriculture, and manufacturing industries. Co-produced by the NFB and Crawley Films Ltd. with the assistance of Atomic Energy of Canada Limited.