A young man dressed as the legendary seducer Don Juan is found about to commit suicide and is subsequently taken to a psychiatric hospital. Here, he meets Dr. Jack Mickler, a psychiatrist on the verge of retirement. The young man, who insists on being called Don Juan, recounts his life story filled with passionate love affairs and adventures that blur the lines between reality and fantasy. His tales captivate Dr. Mickler, who becomes intrigued by the depth and conviction of Don Juan's alter ego. As the sessions progress, Mickler starts to question the boundaries of sanity and whether his patient might genuinely believe in his fantastical identity.

Dr. Mickler, dealing with his own professional doubts and a midlife crisis, finds himself increasingly drawn into Don Juan's romanticized world. Don Juan's infectious passion for life begins to seep into Mickler's own relationships, particularly with his wife Marilyn. These changes lead Mickler to reflect on his long career and personal life. Mickler embarks on a journey of self-discovery, wrestling with the conflict between clinical detachment and emotional empathy. This sets the stage for a deeper exploration of love, identity, and the power of storytelling, challenging both doctor and patient to reevaluate their perceptions of reality and happiness.