A doctor's research into the roots of evil turns him into a hideous depraved fiend.

Ellen Saunders is an heiress on a cruise to Europe being pursued by a day laborer mistaken for a prominent mining engineer. During the cruise, he foils two crooks trying to get their hands on her lucrative nickel mine.

Ziegfeld Follies headliner Billie Burke starred in a handful of silent films, of which Arms and the Girl was the second. Burke plays an American lass who journeys to Europe to be reunited with her fiance. Not only has her sweetheart been unfaithful, but she arrives on the continent just as World War I breaks out.

Ralph Valentine, a penniless pianist, goes to Paris to pursue his career. He is attracted to two women: Pauline, the sweet and innocent daughter of his landlady, and Flora Margot, a woman of loose morals who runs with a wild crowd. Because of his irrational passion for Flora, Ralph makes a bargain with Satan, who gives him a magic skin which gratifies every wish and shrinks, along with the well-being of its possessor, in proportion to the number of wishes realized. Ralph tries in vain to rid himself of the skin after Pauline commits suicide because of his vices. Just as the devil comes to lead him into hell, Ralph awakes with the skin in his hands in an antique store where he had gone to buy a necklace for Flora. He throws down the skin, and runs to Pauline and professes his love for her, happy that he had been only dreaming.