Crescendo (1970)

An innocent project transforms into a perilous nightmare when researcher Susan Roberts arrives in France in search of information on a deceased composer. She contacts his widow whose mental deterioration, precipitated by the death of her husband, manifests itself in psychotic dementia. The young woman's arrival triggers an obsessive desire to marry her crippled son to Susan, ensuring by this union that the genius of the father will be passed on to future generations.