Reliable international intrigue tale, with Capt. Hugh North, dexterous U.S. secret service operator involved in a melee in the Balkans. English, Russians, Roumanians, Poles, Germans are all out after a principle to detonate a new and fierce explosive --the principle is in the hands of the inventor's daughter, a ballerina. With the help of a fellow American, posing as a Contessa, North manages to come through strict surveillance, a murder or two, and all hell breaking loose with bombs to the right and left. Usual sterling fare from Mason.