During the Cold War, a microfilm concealed in the collar of a panther, transported by freight rail, is sought by several spies after the animal escapes its cage following the train's derailment in Switzerland.

Roger Quain, who escorts two zoo-bound black panthers on the train from Milan to Paris, agrees to help a Western agent, Catherine Ullven, by hiding a microfilm in the collar of one of the animals. But, while in the Swiss Alps, the train is derailed, the panthers escape and three enemy agents hunt down the animals, Catherine and Roger. Will they escape them?—Guy Bellinger