In mid-October, Puck Connolly rides her horse, Dove, in the stables. She and her two brothers, Finn and Gabe, live together; they lost their parents a year ago to the capaill uisce while their parents were fishing. Her younger brother, Finn, drives by in his car and signals that he wants to race. Finn rides Dove through the streets of Skarmouth, where she sees her older brother, Gabe, working at the hotel. She loses the race to the beach, where she spots Finn quietly looking at the water. A capall uisce rises out of the water. Each October, the water horses emerge, and men begin catching them to train for the races. To Puck’s relief, this one runs down the beach without approaching them.

Sean, now 19 years old, visits the butcher, Thomas Gratton, and his son, Beech. Beech drains the blood from a cow to sell to Sean for his capall, Corr. Since he was 10, Sean has worked for Benjamin Malvern, who raises sport horses that he sells to the mainland. Sean’s father’s death left him an orphan, as his mother had moved to the mainland the year before.

Thomas informs Sean that the Connolly children recently saw the first water horses emerge from the sea. Sean thinks about how excited he is for the Scorpio Races to finally begin.

That night, Puck and her siblings have dinner. All they could afford were the ingredients for an apple cake. Gabe tells them that he is moving to the mainland in two weeks, adamant that he can no longer deal with living on the island. Puck feels angry and betrayed. Desperate to stop him from going, she tells her siblings that she is going to compete in the Scorpio Races. She hopes that she can win the monetary prize and convince Gabe to stay, though she wonders if she really has the courage to race. Gabe simply responds that he will wait two weeks until after the race.

Sean dreams of the night he caught Corr, feeling a mix of awe and fear at the water horse’s strength. He is woken up by two boys, Brian and Jonathan Caroll. They tell him that Mutt Malvern, the son of Sean’s boss, tried to catch a water horse with his friends and is trapped.

Sean rushes to the beach. He finds Mutt with an older boy, Padgett; the two have a rope tied to a massive capall. When Mutt spots Sean, he yells at him to stay away, insisting that he can handle it. Sean thinks of how little he likes Mutt. He tries to warn him, but when Mutt responds with anger, Sean allows him to struggle with the water horse. The horse breaks free, biting Padgett’s shoulder and crushing him. Sean then intervenes, grabbing the horse’s mane behind the ear and putting a red ribbon in front of its nose. He whispers to it, causing it to finally calm down.

As Sean gets the capall under control, Mutt angrily yells at him not to let it go, insisting that he earned the horse after the damage it caused. Sean briefly considers, noting how he is the only one who could safely bring in the capall. Instead, Sean steps into the water, whispering to the horse and letting it go back into the ocean.

The next morning, Puck wakes up and prepares to go to the beach for the first day of training. In the kitchen, she is surprised to find Finn already awake. He made them both a cup of hot chocolate. It shocks Puck, as she realizes that it is one of the first times he has seemed to care about Puck or their homelife since their parents died. As she looks around the kitchen, she notes how much of a “mess” their life is and isn’t surprised by Gabe’s decision to leave it behind.

Gorry, a horse trainer, calls Sean to the beach early before training starts. He shows him a black and white piebald capall that he hopes Sean’s boss will buy. He insists that she is the fastest one he has ever ridden. Sean immediately dislikes her, noting fierceness and restlessness. However, Sean agrees to ride her. As they move down the beach, Sean notes her impressive speed, wondering if she is faster than Corr. However, the horse then tries to get to the water, forcing Sean to travel in that direction. Sean notes how the horse’s “magic” nearly overwhelms him and convinces him to enter the sea. Instead, he uses all his experience and skill, barely managing to bring the horse back to Gorry.

As Sean dismounts, he insists that he does not want the capall. He advises Gorry to release her back into the ocean because she is dangerous but knows that Gorry won’t listen.

As Puck and Finn arrive at the beach, they look down at the collection of men and horses, a chaotic mess on the shore. She is then distracted by a man (Sean, though Puck does not know him yet) riding a “bright red [capall] like fresh blood” on the edge (44). Finn then points out the massive piebald horse being led away from the group. It screams, chilling Puck.

As she makes her way down to the beach, Puck is overwhelmed by the chaos. She searches for a man wearing a bowler, which is the traditional outfit of “horsemongers” who sell horses. She spots Gorry, who is leading the piebald capall, and approaches him. She asks if he does “fifths,” a practice where a horsemonger will give a rider a water horse and take four-fifths of their winnings in exchange. However, Gorry dismisses her.

Puck spends the rest of the morning trying to find a horsemonger who will back her. They all dismiss her, most laughing at her or refusing even to listen to her. By lunchtime, she sits by the ocean, wondering if she is even capable of riding a water horse. However, she is determined to try, so she returns to Gorry. Now, he only has the piebald capall with him. She again asks if he would be willing to do fifths, noting that he has nothing to worry about if the horse is as speedy as he claims. In response, Gorry invites her to ride it, insisting that she prove she is capable.

Puck stands on a boulder looking at the water horse as Gorry urges her to ride it. She realizes the thing that’s stopping her isn’t fear but the thought of her parents; they hated the races and were killed by capaill uisce, so Puck knows they would be disappointed in her. She looks up and sees Finn watching her. She makes a decision and tells Gorry that she won’t ride the capall. In that moment, however, the horse rears up and grabs a nearby dog. It kills it, tossing part of its body toward Puck, who has fallen from the boulder.

As men yell around Puck and get the capall under control, Finn comes to her. He urges her not to ride a water horse. Puck replies that she has decided to ride Dove in the Scorpio Races.

That night, Sean trains Corr up and down the beach, playing in the water. After, he coaxes Corr from the water, noting how her magic draws her to the Scorpio Sea. He looks up and sees Mutt on the ridge, watching. As Sean grabs his boots, he realizes that Mutt urinated in them. Sean simply empties them out and continues off the beach, not wanting to give Mutt the satisfaction of seeing him bothered.

That night, Puck walks through Skarmouth to the butcher’s to sign up for the races. As she waits in line, she spots Sean nearby and recognizes him as the man riding the red capall. An old man scolds her, insisting that she shouldn’t stare at Sean, who is considered the heavy favorite to win this year. When Puck gets to the front, Peg Gratton, Thomas’s wife, questions her decision to enter the races, but Puck stands firm. She requests a rule sheet and looks through it to confirm that she is allowed to enter with a normal horse. She pays her entry fee and writes down her name alongside Dove’s.

After, as Puck goes to leave, she sees Sean in a tense conversation with Mutt. Mutt accuses him of losing his capall. Sean initially refuses to respond, using his silence as a weapon. Mutt claims that he is going to get Sean fired for “theft,” which finally prompts Sean to speak. He points out that Mutt is only alive because he has kept him alive each year during the races—and he will continue to do so on Mutt’s father’s orders. Gratton arrives and breaks up the confrontation.

Puck dreams of the day her mother taught her to ride a horse. When she wakes up, she feels Gabe standing in the doorway to her bedroom. She desperately hopes that he will come and sit on her bed as he used to before their parents died. Instead, he turns after a few moments and leaves.

Meanwhile, Sean cleans out the stables that house the three capaill uisce because the stable hands are too afraid to do it. He thinks of his desire to have his own ranch one day. However, he knows that he would settle for having only Corr and his own home, not having to answer to Mutt or his family anymore.

The next morning, Puck tries to get Dove from the pasture so that she can take her down to the beach to train, but Dove stubbornly avoids her. A red car pulls up that Puck recognizes as belonging to Father Mooneyham of St. Columba’s Church. Peg gets out and comes to Puck. She and her husband discussed Puck’s entry, and Peg assured him that she would try once more to stop Puck from entering the races—especially with a normal horse. However, Puck again dismisses her, insisting that she has “personal reasons” for entering. Peg sighs in resignation and leaves. Just before the car pulls away, Father Mooneyham calls to Puck, reminding her that she has not been to confession in a long time.

Instead of going down to the beaches to train, Sean is stuck at the ranch entertaining an American horse owner, George Holly. As they watch Corr, Holly asks about Sean’s history, and Sean explains that he has won the Scorpio Races the last four years. Holly praises him, offering Sean a job when he returns to the mainland after the race. When Holly asks about buying Corr, Sean insists that Malvern will not part with him. He thinks of how Malvern will not sell Corr even to Sean, who has offered his share of the winnings from the last four races. Sean decides that he likes Holly, as he clearly has affection for the horses.

On the way to the beach, Puck and Finn stop at a shop owned by a woman named Dory Maud and her sisters. Puck paints teapots that they sell in the shop. Dory is delighted to show her a new catalog that the town printer, Mr. Davidge, made for them. It will allow them to sell their products on the mainland. As the sisters begin to pester Finn, Puck leaves for the beach.

Sean watches Puck on the beach. She is in the water with Dove. He notes the danger of having a horse in the water among the capaill uisce but decides it’s not his problem to worry about. Instead, he takes Corr and two other capaill. He has tried to train the two others, but they are being stubborn.

On the beach, two water horses begin fighting, and one bites the fingers off its owner. The other breaks free in the water and begins making its way down the beach toward Puck. Sean runs quickly down the shore and into the water. He reaches the loose capall just as it attacks Puck, pulling on her sweatshirt and dragging her into the water. With no other choice, Sean draws holly berries, which kill water horses, from his pocket and forces them into the capall’s mouth. As the capall dies, it turns on Sean and throws him into the water. Puck pulls him above the surface. Sean angrily tells her to keep her horse off the beach.

Puck returns home, shaken by the incident. She is adamant that she can’t continue in the race but also fears the judgment and humiliation of backing down. As she debates what to do, Benjamin Malvern comes to her home.

Puck invites Malvern inside and offers him tea, unsure why he is there. As Malvern drinks, he tells Puck that he has come to evict her and her siblings. To Puck’s surprise, their house is not paid off; Gabe has not made payments on it during the last year. Malvern tells her that he came to tell her about the eviction to her face, hoping to enjoy her reaction. He asks her what she and her siblings are “willing to do to save this house” (107). In response, she tells Malvern that she wants to wait until after the races, adamant that she will compete and win. She knows that Malvern will agree, as he will enjoy the spectacle of it.