The Mephisto Waltz (1971)

A frustrated pianist himself, music journalist Myles Clarkson is thrilled to interview virtuoso Duncan Ely. Duncan, however, is terminally ill and not much interested in Myles until noticing that Myles' hands are ideally suited for piano. Suddenly, he can't get enough of his new friend, and Myles' wife, Paula, becomes suspicious of Duncan's intentions. Her suspicions grow when Duncan dies and Myles mysteriously becomes a virtuoso overnight.