The title is taken from a musical piece of the same name by Franz Liszt and is very fitting. Alan Alda plays a somewhat successful writer who is sent to interview the worlds greatest piano player, Duncan Ely (Curt Jergens). Alda's character of Myles Clarkson also plays the piano a bit and Ely encourages him to play more.
Gorgeous Jacqueline Bisset is the wife of Myles and soon she is swept into a web of very bizarre terror. It seems Ely is a Satanist who is dying and he wants to exchange souls with Myles so he can continue to play the piano and be young again.
This is accomplished and Myles goes on to great fame, but his wife notices a lot of differences in him, and soon people start dying including their young daughter Abby (Pamelyn Ferdin). Myles and his new lover Roxanne Delancey, who was also Ely's lover plot to have Myles' wife killed, but it doesn't work.
After a lot of investigation Bisset's character of Paula discovers what is actually happening and decides to try and stop it, but she fails, so she does the next best thing....and that is the very cool twist ending to this early 70's horror gem that was lost in the shuffle after Rosemary's baby was released around the same time.
I will not reveal anymore in case you haven't seen it, but I can recommend this to horror fans. The excellent cast in this Quinn Martin production directed by Paul Wendkos includes Barbara Parkins, Bradford Dillman, William Windom, Khigh Dheigh and Berry Kroeger.
This has also just been released on Blu-ray from Criterion. HIGHLY RECOMMENDED!!