Garden Apartment

Maisie is moving into her first apartment. She always lived at home and feels lucky to find a furnished apartment that leads out to a garden. The previous tenant Cassie, mysteriously just disappeared. Stella lives upstairs, and Maisie thinks she is mean. At night, she hears strange noises. Maisie looks through the keyhole and sees Cassie bound by a leather collar and chains. She thinks Stella is holding her captive.
Instead of calling the police, she decides to free Cassie from Stella's bondage. Can she get Cassie free or will she be captured by Stella? All the characters are over the age of 18; none are related, and all sex is consensual.