The play begins in a hedge-school in Baile Beag, with Manus, the schoolteacher's "lame" son, trying to teach Sarah, a mute girl, to speak. The school is run by Manus' father, Hugh, who teaches the students to speak Irish, Latin and Greek, but not English. Owen, Manus' younger brother, returns home and enters the school to announce he is working for Captain Lancey and Lieutenant Yolland, two English soldiers, helping them create a map of the land which will anglicize the Gaelic names.
Manus is in love with a girl named Maire, but she won't marry him because he doesn't have a proper job. Manus cares for Hugh with great attention because Hugh is almost constantly in a state of drunkenness. Two men arrive in the village to offer Manus a job teaching at a school on a distant island. While he thinks this will convince Maire to finally marry him, Maire now has her sights set on the English soldier, Yolland. Maire and Yolland go to a dance together and kiss, and while they don't speak the same language, they profess their love for one another.
Manus finds out about the kiss, and the next day Yolland goes missing. We learn that the Donnelly brothers, twins who are known to be violent, were seen coming to the dance and left before the end. It is assumed that they kidnapped Yolland or killed him, but no one says for sure. Manus, who is heartbroken about Maire's betrayal, decides to leave home and go away for a while. In the wake of Yolland's disappearance, Captain Lancey declares that if Yolland isn't found within the next 48 hours, the English army will kill the villagers' livestock, then destroy their crops and level their homes. Owen decides to join the resistance. Hugh drunkenly tells Maire he will teach her English, and recites the opening of Virgil's Aeneid.
