Carlo Carlo Giustini is hired as a chauffeur at the English country manor owned by Roger Wynter Ralph Richardson and his wife Judith Wynter Margaret Leighton. Judith is a respected novelist who writes bold, escapist romances for a popular market, yet in everyday life she embodies a steady, unassuming wife, happily married to a husband who has been rendered immobile by polio. She draws on the people around her and the situations they share as raw material for her current project, a novel titled The Passionate Stranger.
As the story unfolds, Judith’s book chronicles a bored, discontented wife who begins an affair with her Italian chauffeur. In a meta twist, the film shows how Judith’s fiction bleeds into reality. One day, Carlo drives Judith to London to meet her publisher, and she leaves a copy of the manuscript in the car. Carlo finds it and begins to read, and the black‑and‑white world of the film gradually gives way to vivid color as the manuscript’s narrative comes to life on screen. In the color sequence, the tale follows Mario, the mistress’s chauffeur, as he drives the woman from London to a village pub. After a tyre blows out, they must rent rooms above a small village pub, while the husband, Lord Hathaway, remains cool and distant, more concerned with the car than with his wife’s feelings. The pair dance at a local fete and, by the end of the evening, Mario has seduced her. When pregnancy is revealed to Lord Hathaway, he is shocked, and the question arises whether Mario should be dismissed or whether the child will be raised as their own. Mario urges the woman to leave her husband and run away with him, yet she remains loyal to the marriage. Undeterred, the plot turns more sinister as Mario schemes to kill the husband, sabotaging his wheelchair and luring him toward a summerhouse with a slope. The plan culminates with the husband floating in the lake, and Judith learns only later that the fiction’s violence has shed its page and entered real life.
When the color returns to black‑and‑white, Carlo becomes convinced that Judith harbors a repressed passion for him. Before a return journey home, he tampers with the car again by adding sugar to the petrol, causing a breakdown; Judith refuses to abandon the vehicle and instead takes a ride with a passing motorist to the nearest village, leaving Carlo behind. Undeterred, he persists in trying to stage conversations and scenes from the book, pressing his suit with growing desperation. His insistence grows confrontational as Judith rejects him, and he proclaims his love while pointing to what he claims is Roger’s inability to father a child. Judith reiterates that she loves her husband, and they have two boys away at boarding school who will return soon.
The tension reaches a pivotal moment when Judith discovers Roger’s wheelchair in the lake. At first, she fears Carlo has enacted the novel’s plot once more, but the truth soon emerges: their son had accidentally driven the wheelchair into the water, and Carlo has heroically rescued him. Grateful for the stand‑up man he has shown, Judith acknowledges Carlo’s lasting affection, yet she remains devoted to Roger. With the emotional storm behind him, Carlo decides to leave. He boards a bus and ends up sitting beside the Wynters’ maid; their eyes meet in a quiet, knowing exchange as the bus pulls away, leaving Carlo to drift between fantasy and reality.
