Roman Polanski's version of Shakespeare's tragedy about a Scottish lord who murders the king and ascends the throne. His wife then begins hallucinating as a result of her guilt complex and the dead king's son conspires to attack MacBeth and expose him for the murderer he is.

Robert and Katherine Thorn seem to have it all. They are happily married and he is the US Ambassador to Great Britain, but they want more than to have children. When Katharine has a stillborn child, Robert is approached by a priest at the hospital who suggests that they take a healthy newborn whose mother has just died in childbirth. Without telling his wife he agrees. After relocating to London, strange events - and the ominous warnings of a priest - lead him to believe that the child he took from that Italian hospital is evil incarnate.