The fourth series of the show commences with Jamie Theakston learning about the former German state executioner Johann Reichhart, who went from dispatching enemies of the Nazis to executing Nazi war criminals.

Jamie Theakston travels to Rome to meet church officials, expert archivists, scholars and authors to uncover some of the historical treasures stored in the Vatican Archives.

Jamie Theakston investigates a shadowy, secret department within the Bulgarian government suspected of carrying out assassinations in nine other countries during the Cold War.

Jamie explores the history of the Knights Templar, attempting to uncover their secrets and speaking to some of those who challenge the accepted traditional view of the order.

Jamie examines the life of Mary Magdalene who, having witnessed Jesus' death and resurrection, is a key but controversial figure within Christianity,

An examination into the murder of Benito Mussolini and possible motivations behind it other than the official story. Theories include his ultimate uselessness to Hitler and the supposed existence of incriminating letters from Churchill.