Act 1

When The Changeling begins, Alsemero has fallen in love with Beatrice, whom he has just met in a church. He intends to cancel his voyage from Alicant, Spain, to Malta, and marry her. When he tells Beatrice of his love, she regrets that five days ago she was promised in marriage to Alonzo de Piracquo.

De Flores enters the scene; he is the servant of Vermandero, Beatrice's father. Beatrice despises De Flores, but he is in love with her and persists in seeing her at every opportunity. When her father enters, Beatrice asks him to invite Alsemero to his castle. Vermandero agrees when he discovers that Alsemero's deceased father was an old friend of his.

The second scene introduces the subplot. Alibius, an old doctor who is in charge of a lunatic asylum, confides in his servant Lollio that he is worried his young wife Isabella may...