Amid Cold War tensions, a gifted nuclear physicist - poised to become the future father of new weapons - shockingly gains religious faith. Seeking to confess this revelation, he enters the priesthood, finding purpose but facing myriad trials. His startling 1970s conversion from secret Soviet weapon scientist to devout priest elicits incomprehension and suspicion on all sides. Colleagues shun him as studies now intermix seminary training with Siberia's nuclear work. His transfer to a lowly role with barred access quashes the prestige of high-stakes research. Friends and family largely abandon the zealous convert, except for his steadfast wife and parents. Ostracized yet undaunted, Father Alexander persists in his ecclesiastical calling even unto Chernobyl's radioactive inferno, ministering to desperate liquidators staring mortality in the face. There, on the fourth block, he was given a nickname - 'Atomic Shepherd'. Upon returning to Moscow, few of them will reach old age. The 'Atomic Shepherd' is the last to leave among his spiritual friends - he still has time to complete his confession.