Female teacher in rope hell (1981)

A female teacher spots one of her students being molested by a vagrant. But her rescue attempt fails as the vagrant drags the teacher into an empty classroom and sexually assaults her. The student finds a school employee, a piano tuner, to try and help but all they can offer is some comfort. Later the piano tuner invites the teacher to his house. He wants her to be his obedient loving bride and has built a nice caged apartment in his basement all for her. He subjects her to an endless series of sexual humiliations to persuade her to say yes.