The Silver Car.

After serving in the Great War, international crook Anthony Trent resolves to go straight. He wants to track down the English private who saved his life, and discovers his true identity is Arthur Grenvil, the son of the Earl of Rosecarrel. Trent falls in love with Grenvil's sister, Daphne, and sets out to win the Earl's approval. He discovers that the Earl is being blackmailed by Count Michael Temesvar, the prime minister of Croatia, over some documents.