Michael Lanyard, reformed jewel thief known as The Lone Wolf, returns to Europe even though he is wanted by police bureaus across the continent. When Michael retires to his hotel room, a woman sneaks in, and he recognizes her as Princess Thania of Arvonne. Michael discovers gems in Thania's purse, but she manages to escape before he can question her. Intrigued by Thania, Michael follows her, and as he listens outside her door, he overhears Grand Duke Gregor, Baroness Gambrell and Marquis Albert de Meyervon blackmail her. Years ago, the Queen Regent loaned the crown jewels to the trio because she was in need of money, but now they refuse to sell the jewels back, and are demanding that the family abdicate or risk exposure that the jewels were lost. Later Michael joins the ball downstairs and, eager to offer his thieving skills for a good cause, offers to help Thania. Thania pretends to rebuff a pass made by Michael, and he leaves with Gambrell. Michael and the baroness go to her room and he manages to open her hidden safe and remove her share of the jewels. Later, Michael diverts Gregor and replaces his share of the jewels with paste replicas. Then, Michael and Thania leave for Arvonne in an airplane, unaware that their pilot is in cahoots with the trio of thieving nobles. The plane lands at Gregor's hunting lodge, and after Michael disembarks, Gregor tortures Thania into telling him where the jewels are hidden by throwing knives at Michael. After the conspirators leave, Michael and Thania escape and arrive in Arvonne in time to help prevent the queen's son from being forced to abdicate. As the Chancellors of the Crown open the vault, Michael pretends to take the jewels, then runs to Gregor and insists they plotted together. Michael's accusation is confirmed by the discovery of the remaining jewels in Gregor's money belt. The boy king is crowned, and the royal family allows Michael, who is grateful for his adventure, but is sorry to leave Thania, to "escape."
