Roger Quain has undertaken a strange task: he is transporting a pair of rare black panthers from Milan to Paris for his uncle, who runs a circus. The night before he leaves his hotel in Italy, Quain answers a knock at his door to find a beautiful young woman, Catherine Talbot, who has an even more extraordinary request. She is a British secret service agent, in possession of some microfilm containing precious deadly information. She needs to get the film out of Italy and back to Britain fast – and the panthers might be the perfect disguise. But when their train is derailed as it crosses the Swiss Alps, the panthers – and the microfilm – go missing.
The search in the wild mountain range attracts hunters from far and wide – but whether they’re hunting the panthers, or the microfilm, Quain and Catherine cannot tell . . . and their enemies may be closer than they think.