
Immediately after the dream, in which a blue substance is placed on Abby's forehead, Paula finds the blue substance actually on her daughter's skin. Duncan tells her that he does not want to harm the girl, but that his Master has insisted upon it as "part of the bargain". Paula has a nightmare in which she envisions Duncan telling her that he must kill Abby, her and Myles' young daughter. Myles soon is pursuing a career as a pianist and is so successful that he is able to take over Duncan's concert schedule.

Though confused by the change in her husband, she also finds his new persona exciting and attractive. Myles' ensuing change in personality, which includes his now being able to play the piano as well as had Duncan, is noticed by Paula, but she is initially unsuspecting of the cause. As Duncan's physical body nears its end, father and daughter perform an occult ritual that transfers Duncan's consciousness into Myles' body while Myles’ consciousness is transferred into the body of Duncan as he dies. Unbeknownst to them, Duncan and Roxanne are Satanists. While Paula is disturbed by the level of attention being paid to them, Myles is honored to be considered a friend by Duncan, who is dying of leukemia. Paula does not much like Duncan and especially dislikes Roxanne. From that point, Duncan and his adult daughter, Roxanne, strongly pursue a friendship with Myles and wife Paula. At first annoyed by Myles' presence, Duncan notices that Myles' hands seem perfect for the piano. Myles Clarkson, long ago frustrated in his hope for a career as a concert pianist, is now a music journalist and interviews Duncan Ely, perhaps the world's greatest piano virtuoso. The film was the only big-screen work of veteran television producer Quinn Martin.



Ben Maddow adapted his screenplay from the novel of the same title by Fred Mustard Stewart. The name of the film is taken from the piano work by Franz Liszt of the same title (see Mephisto Waltzes). It was directed by Paul Wendkos and starred Alan Alda, Jacqueline Bisset, Barbara Parkins, Bradford Dillman and Curt Jürgens. The Mephisto Waltz is a 1971 American horror film about an occult-murder mystery.
