In the chaotic world of phobias, Bob Wiley struggles to find peace within the confines of his New York City apartment, which has turned into a veritable prison. Despite his regular therapy sessions, his journey towards healing seems like a constant uphill battle. His therapists, increasingly frustrated by his incessant neediness and intrusions, ultimately send him to seek help from the self-centered Dr. Leo Marvin. Initially excited by Leo's recent book, Baby Steps, Bob feels a spark of hope during their first session. However, his optimism is short-lived when Leo, eager for a family vacation, brushes him off after their initial meeting, leaving Bob in a state of despair.
Determined to reconnect, Bob resorts to some unorthodox methods, even impersonating Leo's sister to get through to him. Yet when he reveals his true self, he only faces further rejection. Leo advises Bob to "take a vacation" from his troubles, a statement that marks what seems to be a turning point in their therapeutic relationship. Curiously enough, Bob announces his own vacation plans, heading to Lake Winnipesaukee, New Hampshire, where fate intertwines their lives as he becomes a guest of the Guttmans, a family that holds a longstanding grudge against Leo for acquiring land they once coveted.
At the lake, while Leo attempts to keep his distance, Bob forms genuine connections with Leo's family, including Anna and Siggy. His natural charisma uplifts those around him as he encourages Siggy to confront his fear of diving—a feat Leo himself had struggled with. However, things take a turn when Leo impulsively pushes Bob into the water, prompting a rift that is only smoothed over by his wife Fay, who invites Bob to dinner. A thunderstorm forces Bob to stay overnight, during which he begins to confront his germaphobia, slowly relaxing his compulsive need to sanitize everything around him.
As Leo's jealousy builds due to Bob's growing popularity with the Guttmans, a live interview opportunity with Good Morning America presents itself. Leo’s efforts to keep Bob away backfire spectacularly when Bob’s enthusiasm and authenticity eclipse Leo, leaving him humiliated. In Leo's desperate attempt to regain control, he concocts a plan to have Bob committed, but Bob's charm seals his fate with the hospital staff instead.
In an act of desperation, Leo eventually resorts to kidnapping Bob, shoving him deep into the woods while brandishing a shotgun and explosives he refers to as his twisted version of "death therapy." However, Bob cleverly applies Leo’s "Baby Steps" philosophy to free himself, leaving him rejuvenated yet concerned for Leo. Upon returning to the Marvin household, Bob commends Leo for his pivotal role in his transformation, unaware that Leo is already plotting his escape from the mess he created.
The situation reaches its climax when Leo's neglect leads to a calamitous explosion at his home, resulting in his subsequent institutionalization. In a surprising twist, Bob marries Lily, Leo's sister, and during their wedding, Leo, momentarily waking from his stupor, screams in dismay as he realizes his new reality: Bob is now his brother-in-law.
In the end, the story wraps up with Bob returning to academia, ultimately becoming a psychologist and authoring a best-selling book titled Death Therapy, much to Leo's furry as he ends up embroiled in a legal battle over the rights to the title.
