How does Ramotswe get Ranta to change his position on the Curtin story and talk to her?

Ranta says at first that he knows nothing about the disappearance of Michale Curtin and that he told the police everything he knew. Mma Ramotswe feels he is lying and tells him that. He tells her to leave or he will call security and say she was trying to steal something. She tells him she knows about a girl named Angel and what he did to her examination. He tells her to come to his house that evening and he will tell her the story.