Lucas Vieira is trying to close a 20 billion dollar deal with a Russian businessman. The problem is the man uses his wife as a translator and the wife has her eyes set on an affair with Lucas. In a pinch, and with time running out, Lucas needs a woman who will act as a translator and also as his mistress to head the wife off. His assistant recommends a woman he knows (who just happens to be a call girl). The call girl already has plans so she passes the buck onto our heroine (Caroline), her fellow classmate (who is oblivious to her friend's true profession). She offers Caroline $500 to act as translator and pose as Lucas' mistress.
Long story short, Lucas ends up believing that Caroline is a prostitute, and that thought pretty much stays with him (in the background) throughout the story.
The story is propelled forward by the fact that after sleeping with Caroline after their first meeting and thinking she got paid to have sex with him, he went to confront her, and, finding out that a man had just broken into her apartment, urges her to move in with him.