The Secret of St. Ives (1949)

Anatole de Keroual is captured by the British in the Napoleonic war and imprisoned in the dungeon of Edinburgh Castle with six companions. Floria Gilchrist, coveted by the fortress commander, Major Edward Chevenish, falls in love with Anatole, and he with her, but Chevenish refuses Floria's plea for a pardon for Anatole unless she agrees to marry him. Anatole engineers an escape from the prison, and goes to London to straighten out affairs of the estate of his uncle, Viscount Victor St. Ives. There he is apprehended and put on trial for murder.