George Nader seems miscast and out of place in this Grade B adventure. He sports a dainty mustache, is wrapped in 17th-century costumes, and has little opportunity to display any of his on-screen charm. What's worse, he never once gets to take his shirt off. What's a George Nader without some good ol', all-American "beefcake?" The plot here is routine and while there's a bit of swordplay, the movie's modest budget keeps everything disappointingly small-scale and constricted. (The fact that only D'Artagnan and Porthos show up from the original "Three Musketeers" indicates that corners are being cut.) The result isn't so much bad as just oh-so-forgettable, and if you're wondering what the "Secret Mark" of the title is, it refers to the "X" which our hero cuts into the foreheads of his enemies with the tip of his sword.