Summary
Steve Quain, escorting two zoo-bound black panthers on a train from Milan to Paris, is unaware that a secret agent, Catherine Ullven, has concealed an incriminating microfilm in the collar of one of the animals. But when the train is derailed in the Swiss Alps and the panthers escape, she is forced to involve him in her mission, which includes enemy spies hunting the microfilm, the animals, Catherine and Steve.