The story takes place on the Riviera, where the title character may or may not be involved in various shades of skullduggery, including murder.

Mathilde Strangerson, the daughter of an eminent scientist, narrowly escapes being murdered in her own bedroom by an unknown assailant. As the room was locked from the inside, no one can understand how the attacker managed to enter or leave the room. Reporter and amateur sleuth Joseph Rouletabille arrives on the scene to protect Mathilde and resolve the mystery of the yellow room.