The play takes place in "the present" and Act 1, Scene 1 opens "on the Bog of Cats," which playwright Marina Carr describes as "a bleak white landscape of ice and snow." A violin is playing as Hester Swane drags the corpse of a black swan through the snow. The Ghost Fancier watches her and introduces himself, asking if she's ever seen a ghost. Hester tells him the swan is "auld Black Wing," who welcomed her home once when she returned from a time away from the Bog of Cats.
The Ghost Fancier suggests that it's bad luck to mess with black swans, but Hester thinks this is only a superstition, and insists on burying the swan. She tells the Ghost Fancier that she used to live in the caravan nearby, but now she lives in a house up the road. When the Ghost Fancier tells Hester he is looking for Hester Swane, she tells him that she is Hester, and he is surprised, as he thought Hester was dead.
Hester tells him that it's dawn, and the Ghost Fancier realizes that he is too early. This alarms Hester, who realizes that the Ghost Fancier thinks she will be dead by dusk. As the Ghost Fancier walks away, Hester tries to get more answers, saying she cannot die, as she has a daughter. The Ghost Fancier disappears as Monica, Hester's 60-year-old neighbor, enters. Hester tries to point out the Ghost Fancier, but Monica cannot see him.
Monica offers to take Josie, Hester's daughter, somewhere for breakfast, but Hester says that Josie is still sleeping. Monica urges Hester to put her life back together, but Hester insists that she was not the person to make it such a mess in the first place. Monica talks about the fact that Hester's former lover is getting married to Caroline Cassidy, a much younger local woman, and that they want to seize everything that's Hester's. Hester says that everyone has always doubted her for being upwardly mobile, but that her former lover, Carthage Kilbride will always be hers. "...I'm not runnin' with me tail between me legs just because certain people wants me out of their way," she says.
Hester imagines that Carthage will return, but Monica insists that he isn't coming back. As Hester goes to bury Black Wing before Josie wakes up, Monica says she will be back later to help her pack, even though Hester insists that she will not be packing.
Scene 2. Josie, age seven, comes out into the snow in pajamas, singing a song about the Bog of Cats. Mrs. Kilbride, Carthage's mother and Josie's grandmother, enters and tells Josie to go in the house and get dressed.
Scene 3. Hester enters near the caravan and digs a grave for the swan. Suddenly, the Catwoman, "in her late 50s, stained a streaky brown from the bog, a coat of cat fur that reaches to the ground, studded with cats' eyes and cats' paws," and blind, enters. She asks Hester what she is doing, as she is the Keeper of the Bog of Cats. Hester tells the Catwoman to bring back a garden chair she stole, and Catwoman agrees, before producing a mouse from her pocket.
"I need mice the way you need whiskey," Catwoman says to Hester, before telling her she had a vision of Hester riding on a black train through the Bog of Cats and burning it to the ground. She tells her that if she does not leave by the evening she will die, but Hester does not seem to care. "You're my match in witchery, Hester," says Catwoman, "...same as your mother was, it may even be ya surpass us both and the way ya go on as if God only gave ya a little frog of a brain instead of the gift of seein' things as they are, not as they should be, but exactly as they are."
The Catwoman talks about how Hester has a lot of potential but is squandering it, and Hester asks about her mother, whose name was Josie. We learn that Josie got "small and bitter and mean" and left Hester behind at some point. Catwoman tells Hester that the night she was born, Josie took her over to the black swan's lair, and laid her in a nest next to Black Wing. When Catwoman asked Josie why she did that, Josie said that Hester would live as long as Black Wing, not a day more or less. Catwoman tells Hester that every time Josie would put her in the swan's nest, she would come and take her in for the night.
Hester suspects Catwoman of lying to her, but Catwoman insists that she just wants to inform her what her mother was like. "Just forget about her and lave this place now or ya never will," Catwoman says. Catwoman suggests that she has always had the gift of prophecy, but that no one ever listens to her, listing all of the predictions she has made that have come true.
The play begins in an eerie, otherworldly realm. It takes place in Ireland, in "the present," but this present is an almost mythic location, "the Bog of Cats," and the first image is that of Hester Swane dragging a bleeding dead black swan through the white snow of the landscape, before striking up a conversation with someone known as the "Ghost Fancier." Marina Carr's theatrical world is one in which the supernatural is real, in which the barrier between the world of the living and the world of the dead is breeched, and in which the symbolic and the literal worlds collide. While Hester shrugs off the Ghost Fancier's warnings about bad omens as "an auld superstition to keep people afraid," one cannot help but wonder if in Carr's world, superstitions are well-founded.
The conflict of the play is set into motion rather quickly, as Hester realizes that the Ghost Fancier has arrived for her, but that he is too early in the day, which would suggest that she will die by dusk. He rushes off without an explanation as Hester yells after him, "I can't die—I have a daughter." This sets the plot of the play into motion. Hester Swane, a young woman who is just going about her life, receives a prophecy telling her that she will die by the end of the day, but no more information on the subject.
After introducing the otherworldly and supernatural elements of the plot, Carr snaps the play into more realistic territory. Monica, Hester's neighbor, comes over to share some gossip and encourage Hester to get on with her life and move on from the dissolution of her relationship to Carthage Kilbride. Hester and Monica chat animatedly about the fact that Carthage has moved on, but Hester is intent on the fact that she will be the one to discard the relationship, not him. "I'm the one who chooses and discards, not him, and certainly not any of yees," she insists, asserting herself, in spite of her apparent vulnerability and desperation.
No sooner have the more realistic elements of the plot been introduced than the mystical and supernatural world encroaches once again. The mystical elements of the play typically follow Hester when she is alone. As she goes to bury the black swan, she encounters the Catwoman, a mystical figure who believes herself to preside over the Bog of Cats, and seems to be half-woman and half-cat. She eats mice and wears a strange coat made up of cat parts. Yet again, we see that Hester is visited by all kinds of mystical creatures and beings.
In this section, we see that Hester's mystical connection to the environment and the magical elements around them at the bog was passed down to her by her mother. Catwoman tells Hester that Josie Swane, Hester's mother, was also mystical and gifted in her connection to the natural world around her. Catwoman goes on some long monologues about Josie's unusual parenting, detailing how she laid Hester with Black Wing as a baby and decreed that Hester would not live a day longer than the black swan. We also learn that Josie abandoned Hester when she was only seven years old. Hester's connection to her mother Josie is a complex one, and seems to parallel the fact that she has her own seven-year-old daughter now, who she named for her negligent mother.