The Merchant of Venice.

A rich merchant, Antonio is depressed for no good reason, until his good friend Bassanio comes to tell him how he's in love with Portia. Portia's father has died and left a very strange will: only the man that picks the correct casket out of three (silver, gold, and lead) can marry her. Bassanio, unfortunately, is strapped for cash with which to go wooing, and Antonio wants to help, so Antonio borrows the money from Shylock, the money-lender. But Shylock has been nursing a grudge against Antonio's insults, and makes unusual terms to the loan. And when Antonio's business fails, those terms threaten his life, and it's up to Bassanio and Portia to save him.