Thérèse Arnaud, a.k.a. Agent C.25, is a member of the French Deuxième Bureau secret service tasked with fighting enemy spies operating in WWI France. She is a thoroughly modern woman: independent, intelligent, sure of herself and of her calling. She deploys and controls her own network of sub-agents and poses as Mademoiselle Janine Félerat in Parisian high society.

Thérèse Arnaud, the creation of mystery writer Pierre Yrondy, is one of the few long-standing female characters in popular French literature. Her adventures were published in 65 magazines in 1934-36, and reprinted in 1946. The eight episodes translated in this collection include Thérèse's epic battle against German spies Karl Himmelfeld, Mademoiselle Doktor, and the notorious Mata Hari.