The Secret Mark of D'Artagnan borrows a handful of the characters and little else from the works of Dumas. Like many Italian films of the early 1960s, this swashbuckler stars an American actor, George Nader, in hopes of broadening its market. Nader plays D'Artagnan along more mature lines than most actors; he's even something of a ladies' man, a fact which very nearly gets him killed on several occasions. Confounding D'Artagnan's efforts to work on behalf of Louis XIII is Magali Noel as a buxom Milady De Winter.