Sean Kendrick is as cool as a sea cucumber. Any other kid who sees his dad get eaten by a capall uisce would swear off going to the beach forever, but Sean gets a job raising and riding the beasts. This comes as no surprise, given how he tells us on the first page, "I live and breathe the beach" (Prologue.4) and "I am so, so alive" (Prologue.5). The kid is addicted to the life-or-death adrenaline rush that comes with the capaill.
However, do you find it a little strange that Sean never reacts to seeing his father die? He basically writes it off as Dad died because he was scared, and now I'll never be scared of anything. Isn't it possible to not be afraid and still mourn the loss of a loved one?
As an adult, Sean has more feelings for Corr, his horse, than he ever had for his father. And he feels insanely guilty at having to kill a capall, even when the capall is putting another human in danger. In fact, Sean is so overwhelmed by the death of a capall, he sees "colors without any name flicker at the corner of my vision" (18.9). What's with the kaleidoscopic colors? When Sean's dad died, he barely felt anything, yet the death of a horse causes him to hallucinate. Does he just love horses more than people?
Working at the stables isn't just a job for Sean; it's a way of life. He tries to be modest, telling George Holly, "I just ride the horses" (25.11). Talk about an understatement. Sean is one of the few people who seems almost immune to the magic of the water horses. He can simply talk to them and calm them down. The stables would collapse without him. Even when he tries to quit, the rest of the crew knows that Sean is an invaluable part of the team.
That's the one benefit to devoting yourself entirely to your job and not having a social life: You become a sought-after commodity. Benjamin Malvern, the stable owner, doesn't want to let Sean go; George Holly tries to lure Sean to America; and Sean catches Puck's eye with his expertise. Although Sean starts to care for Puck, the person at the core of Sean's heart isn't a person at all: It's Corr. He won't go anywhere or do anything without his trusty steed.
Sean's close association with the capaill is starting to rub off on him. When Puck first gets a close look at Sean, she says he "looks like a wild animal. Not a friendly one" (23.44). He's bristly toward her, and she toward him, but he starts to warm up to her when he sees how similar they are.
He sees Puck as a mirror image of himself (hopefully one that looks less horse-y). He says, "I feel myself being fascinated and repelled by her: She's both a mirror of myself and a door to part of this island that I'm not" (33.58). The "part of the island that [Sean's] not" could very well be the human part of it. Sean has isolated himself with the horses and barely socializes with people—it takes Puck to bring him out of his shell. Or out of his barn, as the case may be. When Puck invites him over for dinner, he starts to open up. He learns about Puck, her history, and her family. There's even some smooching involved. And by forging an alliance with a human, Sean and Puck both end up winners of the Scorpio Races, and they both get what they want: Their horses, and each other. It's so sweet we just might neigh with delight.