A fateful encounter in a Montecarlo casino sees an English widow mesmerised by a young Polish artistocrat. A frenzied twenty-four hours ensue, as both struggle in the grip of irresistible obsessions that drive them to defy the conventions of society, and to risk everything they possess.

Set in the 1950s against the backdrop of Grace Kelly's whirlwind romance and unforgettable wedding to Prince Rainier of Monaco. Movie stars and paparazzi flock to Cannes, but Grace Kelly, the biggest star of all, wants only to escape from the flash-bulbs. When struggling perfumer Sophie Duval shelters Miss Kelly in her boutique to fend off a persistent photographer, a bond is forged between the two women and sets in motion a chain of events that stretches across thirty years of friendship, love, and tragedy.