Riders to the Sea takes place in the kitchen of a cottage located in the Aran Islands to the west of Ireland. As the play opens, Cathleen, a girl of around twenty, is attending to household chores. Her younger sister Nora enters carrying a cloth bundle. Affirming that Maurya, their elderly mother, is in the other room lying down, Nora presents the bundle, which contains clothing that may belong to their brother Michael who has not returned from a voyage on the sea. The two girls worry about the storm brewing outside, since their last surviving brother Bartley intends to go on the sea that day. They decide not to open the bundle in case Maurya comes in, since they are worried about her reaction to evidence of Michael’s death.
Cathleen hides the bundle just before Maurya enters, and Maurya inquires about Bartley’s whereabouts. Maurya declares that Bartley will not go to sea today due to the storm, but Bartley soon comes in to prepare for his voyage and his mother’s attempts to dissuade him from leaving have no effect. Bartley begins to instruct Cathleen on how to do additional chores, such as taking care of the sheep, now that their brother Michael is gone and Bartley, the only man left, will be out on the sea for several days.
Once Bartley is gone, Maurya cries out that he will die by nightfall. Cathleen chastises Maurya for her pessimism and for not giving Bartley a blessing, but then she realizes that she and Nora forgot to give Bartley his bread. She sends Maurya to catch Bartley before he leaves and give him both the bread and her blessing.
Cathleen and Nora quickly investigate the stocking from the bundle while Maurya is gone. They identify it as Michael’s and mourn his lonely death on the sea. A silent, frightened Maurya returns, still holding the bread, and begins to keen, unable to answer Cathleen’s questions about Bartley. Finally, Maurya reveals that she has seen a vision of Michael’s ghost riding behind Bartley, and Cathleen begins to keen as well, interpreting the vision as an omen that Bartley will die. Maurya then reflects on the deaths of all of the men in her life.
Nora and Cathleen hear a crying out by the sea shore. Old women begin to enter the cottage in mourning. Cathleen wonders if they have found Michael, and she gives Maurya the clothes from the bundle as proof of his death. However, one of the women affirms that it is Bartley who has died—he has been thrown by his horse into the sea, and his body is brought in by other townsfolk. In a trance-like state, Maurya sprinkles Holy Water and prays over Bartley’s body, implying that she will die soon now that all of the men in her life are dead.