The film confronts weighty themes concerning existence and substance dependency. Ed Avery, portrayed by James Mason, suffers from a severe ailment that necessitates cortisone treatment—a drug still under experimentation, and one which produces psychological repercussions. Initially, Ed is presented as an intelligent, energetic, and content individual. He leads an unremarkable but pleasant life, grappling with financial difficulties common to many, and the film’s opening scenes illustrate his deep affection for his family and his willingness to protect his wife and sons. Subsequently, he develops a cortisone addiction, fundamentally altering his circumstances and leaving a mark on their lives. Like any habit-forming prescription medication, an intense need to take it consumes him. He even goes so far as to pretend to be a physician in order to obtain the drug. His son and wife are profoundly impacted by his behavior; his son, distressed watching his father descend into depression and fragility, attempts to steal his pills. Ed discovers this act and deliberately leaves his child alone to consider the severity of his actions. He then experiences a religious revelation, specifically referencing the biblical story of Abraham and Isaac. A misguided notion takes hold that he must rectify things by killing his son, followed by his wife, and ultimately himself. Fortunately, he is prevented from carrying out this plan, and the film concludes with a positive resolution as he returns to a semblance of normalcy and his previously happy family life.

Source on TMDB