The plot centers on , a sophisticated young woman traveling by train to Switzerland. Her life takes a dangerous turn when a secret agent, just before being murdered, entrusts her with a piece of jewelry—a panther-shaped jewel with ruby eyes .
Despite the peril, Marie-Chantal remains "cool-as-ice," using her cunning and "panther-like" instincts to outwit her pursuers.
Marie-Chantal is hunted across international borders by Russian and American spies, all vying for the virus.
A Spaniard named Paco eventually comes to her aid, helping her escape several terrifying and comedic situations.