Schoolteacher Ed Avery is a devoted family man who moonlights as a cab dispatcher to support his wife Lou and young son Richie. When Ed begins to experience excruciating pains pulsing throughout his body, he tries to hide his condition from Lou until one night, after a bridge game, he collapses in agony. Upon learning that Ed has been enduring these spasms for months, his physician, Dr. Norton, calls in a specialist, Dr. Ruric, who puts Ed through a battery of tests that reveal that he is afflicted with a rare, deadly blood disease. When Ruric concludes that Ed's only hope lies in taking the experimental drug cortisone, Ed begins treatment under hospital supervision. Several weeks later, Ed is released from the hospital, and Norton cautions him that his drug dosage needs to be closely monitored and that he should immediately report any unusual symptoms. On his first day home, Ed ebulliently ushers Lou to an expensive dress store and insists that she purchase two frocks they can ill afford. When Ed begins to experience drastic mood swings that veer from manic depression to delusions of grandiosity, Lou suggests that he consult Norton, but he protests that he cannot afford to be sick again and begins to increase his dosage of cortisone. At a PTA meeting, Ed deliberately insults both the parents and their children, causing his good friend, gym teacher Wally Gibbs, to become concerned. When Wally visits Lou to tell her about her husband's strange behavior, Ed makes a snide remark about Wally's interest in Lou, then declares that he is tired of petty domesticity and his marriage. After telling Lou that she is his intellectual inferior, Ed relents and agrees to stay married for the sake of his son. Having consumed his entire prescription of cortisone, Ed poses as a doctor and forges a new prescription at a drug store. While playing football with Richie, Ed pushes the boy beyond his endurance, frightening Lou. Soon after, Wally shows Lou an article describing psychosis as a complication of cortisone consumption, but Lou fears that Ed will die without the drug. As Ed's condition deteriorates, he continues to torment Richie, browbeating him about mathematical problems late into the night and driving him to tears. At dinner, Ed launches into a paranoid rant against Lou. Desperate to stop his father from taking more pills, Richie raids the medicine cabinet, but Ed catches him and calls him a thief. As Richie cowers in his bedroom, Lou phones Wally for help, but is forced to leave a message because he is not at home. Decreeing that Richie considers himself above the law, Ed reads a passage in the Bible about Abraham sacrificing his son Isaac. When Lou begs Ed to spare Richie, he declares that they will all die together. After Lou tries to stall Ed, he locks her in a closet, turns up the volume on the television set and then charges up the stairs to Richie's room, scissors in hand. When Ed begins to hallucinate, Richie slips out the door just as Wally bursts into the house and wrests the scissors from Ed's hands. After Wally knocks Ed unconscious, Lou phones the doctor, who heavily sedates Ed in the hospital. Explaining that Ed is suffering from a psychosis induced by an overdose of cortisone, Norton warns that he may never return to normal. After stating that Ed will recover only if he remembers what has happened, Norton agrees to allow Lou to see her husband. In his hospital room, Ed awakens, disoriented, but soon recognizes Lou and Richie, and recalling the disastrous events of recent weeks, gratefully embraces his family.