In post-war Europe, a diverse group of passengers aboard a U.S. Army train to bombed-out Frankfurt becomes involved in a Nazi assassination plot.

In New York, Sheila Bennet and her spouse, Matt Krane, are trying to unload a trove of rare jewels they smuggled into America from Cuba, but the police are hot on the couple's trail. Meanwhile, government officials begin a desperate search for an unknown individual who is infecting the city with smallpox.