In Paris, a private detective named Claude Chavasse leads a thriving business uncovering the infidelities of spouses. Claude’s daughter, Ariane, becomes fascinated by the case of Frank Flannagan, a suave American business magnate and notorious womanizer. One day, while eavesdropping on one of her father's clients planning to harm Flannagan for consorting with his wife, Ariane decides to intervene and warn him. This intervention quickly leads to an unexpected encounter between the young, idealistic Ariane and the experienced, world-weary Flannagan.

Ariane, pretending to be an equally worldly woman, invents stories about numerous admirers to pique Flannagan's interest. Intrigued by her mysterious persona, Flannagan finds himself drawn to her unique charm and wit. The two begin a playful, romantic liaison marked by afternoon rendezvous in luxurious settings. As their connection deepens, both struggle with the secret lives and hidden truths that lie beneath their flirtatious facade. The relationship teeters on profound revelations that threaten to unravel everything Ariane has crafted in her quest to connect with someone she idealizes.