Kind Lady (1951)

When aging art collector Mary Herries (Ethel Barrymore) invites struggling young painter Henry Elcott (Maurice Evans) and his ailing wife, Ada (Betsy Blair), into her home, she little suspects their plan. Henry holds Mary hostage in her own home, posing as her nephew, and telling everyone she's suffered a breakdown. To complete the ruse, he brings in another couple (Angela Lansbury, Keenan Wynn) to pose as maid and butler while he sells off all of Mary's priceless artworks.