This is in almost every aspect a truly amazing film, and there are many odd things contributing to make it unique in its way. The main players and attractions are not Howard Duff and Marta Toren with all their retinue but the two black panthers, that break loose from a train in Switzerland and terrorize the entire landscape, forcing the army to go to war against them and shoot them dead at any cost, while they are invaluable to Howard Duff, their keeper who lost them, and Marta Toren, who used one of them for a spy message. The intrigue is equally masterly contrived, many parts getting involved in this thing, and several of them not hesitating to kill for their business. Walter Slezak, as the inn-keeper, is the one outsider who is totally innocent and provides a charming character for a change and picturesque addition to the stew. It's difficult to follow all the ways and intrigues and turnings of various spies and agents, which it is impossible to discern immediately who is on which side, but some of them come out alive. It's a delicious piece of cake quite out of the ordinary, there is no other spy thriller like it, but its most rewarding qualities are the marvellous shots from the hunting parties in the Swiss Alps, reminding of great natural documentaries, like those of the Swede Arne Sucksdorff, and also of Frank Borzage's "Mortal Storm" ten years earlier.