The play opens in the king’s palace in Naples in the 14th century. It’s nighttime. The duchess, Isabela, has invited her lover, Duke Octavio, to her room but the man with her is in fact Don Juan. When Isabela realises it’s not Don Octavio, she screams for help.
The king arrives, carrying a candlestick. Summing up the situation, he calls for the guards and orders “this man” (l. 26) to be arrested. The guards arrive accompanied by Don Pedro Tenorio, Spanish Ambassador to Naples and Don Juan’s uncle. The king, without ascertaining Don Juan’s identity, orders Don Pedro to punish the intruder and leaves. When Don Juan reveals that he is related to the Spanish ambassador, Don Pedro orders everyone else to leave (l. 46).
Alone with Don Pedro, Don Juan then discloses (l. 54) that he is his (i.e. Don Pedro’s) nephew. Angry, Don Pedro asks for explanations. Don Juan excuses himself saying that he is young, and that since his uncle was young once he should understand. He then admits that he deceived and seduced Isabela by pretending to be Don Octavio (ll. 67-71). Don Pedro cuts him off, and in an aside reveals that this not the first time that Don Juan has deceived women and that his father had sent him from Castile for that reason.
However, instead of punishing Don Juan, Don Pedro lets him escape and advises him to head for Sicily or Milan. As he departs, Don Juan –in an aside— discloses that he is going to return to Spain.
A conversation follows between Don Pedro and the king (ll. 121-57), in which Don Pedro lies, saying that Don Juan escaped over a balcony, defending himself valiantly against the guards. He compounds the lie adding that the deceived woman was Isabela and that she was seduced by Duke Octavio (ll. 146-151).
The king sends for Isabela (l. 138) and accuses her of profaning the palace by her actions. He then orders her to be imprisoned without allowing her to explain or defend herself. At the same