The Collector [1965] William Wyler

Freddie Clegg isn't sure if he can carry out his plan for "her" until he stumbles across an isolated house for sale in the English countryside, the house he spots while he's butterfly collecting. The "her" is London based art student Miranda Grey, the plan to kidnap and hold her captive. Much like he loves his butterflies, Freddie loves Miranda, but from afar. In his mind, his love for her is based on respect for her as a person and not physical lust. So when he does manage to kidnap her and hold her hostage in the basement of his newly purchased house, she, not knowing who he is, is surprised that he is neither looking for ransom money or to sexually assault or rape her. He tries to respect her wishes except the most important wish of letting her go. As she tries to understand what he wants from her, they negotiate the terms of her captivity. All the while, she tries how best to escape while maintaining her safety while in the precarious position of being captive.