Is There Anybody There?

A beautiful woman, Kate (Tina Grenville), is released from a sanatorium unaware that while she was away her husband John (George Lazenby) has begun an affair with her sister Marianne (Wendy Hughes). The two sisters live together in a creepy apartment block while John is away, and find themselves stalked by some mysterious strangers, Rosa (Chantal Contouri) and Duncan (Patrick Ward).