Link (1986)

Jane Chase, a recent graduate, accepts a position assisting an unconventional zoology professor. His isolated estate is home to two highly intelligent chimpanzees and Link, an aging orangutan who serves as butler. The idyllic setting shatters when one chimpanzee dies, followed by the professor's baffling disappearance. Suddenly, Link's demeanor shifts, and he becomes menacingly hostile toward Jane. The playful facade crumbles, revealing a sinister undercurrent, and a terrifying ordeal is about to unfold.