Mark (Sam Neill) and his wife, Anna (Isabelle Adjani) appear to be leading a healthy and happy marriage.
Yet on his return from a business trip in Munich, Mark finds Anna preparing to leave him. Jumping to the conclusion that the reason behind this estrangement is another man - Mark decides to follow his wife to get to the bottom of her decision.
However, on following her he gradually becomes aware of the truth of her departure and discovers more and more strange behaviours and bizarre incidents that indicate there is something other than just a simple affiar.
It soon turns out that she has also left her lover, Heinrich (Heinz Bennent), for a supernatural encounter with a strange creature in an empty apartment.