When a man discovers a beautiful woman in his net, his daughter convinces him that she’s a mystical selkie. However, a mysterious figure comes looking for the woman, turning their fairytale complicated and dangerous. A fisherman named Syracuse is hauling his net into his boat, only to find a woman inside.
When he sees that the woman is alive, he quickly frees and resuscitates her. Immediately, the woman gasps for breath, so the fisherman brings her to the cabin, promising to take her to the hospital. The woman refuses to see anyone except him, and when another boat passes by, she hides.
Curious, Syracuse asks for her name, but the woman claims that she doesn’t know. Assuming that she lost her memory when she fell in the water, he introduces himself, adding that most people call him “Circus” since they think he’s a clown. When he insists on taking her to the hospital, the woman tries to jump off the boat.
The man stops her and promises to take her where no one will see her. He soon takes her to his deceased mother’s caravan, sharing that his mother was a loner and didn’t like people, so no one knows the place. When he leaves, he’s disappointed that the woman doesn’t even say goodbye.
Syracuse rushes to the house of his ex-wife, Maura, to pick up their daughter, Annie. Maura scolds him for being late, but Syracuse ignores her and takes their daughter to her dialysis appointment. During her dialysis, Annie asks for a story to pass the time, so Syracuse tells her about his encounter that day, masquerading it as a fairy tale.
His daughter wonders if the woman was a mermaid or a selkie. Unfamiliar with this word, Syracuse asks what a selkie is, so Annie explains that it’s a seal woman who can sing. The selkie would occasionally leave the sea, lose her seal coat, and live on land until the sea calls her back.
After the dialysis, the nurse surprises Annie with a new powerchair donated by the CRC. Excited, the girl shows it off to her mother’s boyfriend, Alex, when they return home. The following day, Syracuse heads to the caravan and finds the mysterious woman singing by the stream.
He then prepares his boat to go fishing, and the woman insists on joining him. He refuses, believing that it’s unlucky to have a woman on a fishing boat. She challenges this by asking if he’d had luck recently, which Syracuse admits that he hasn’t.
With that, he allows her to join him. During their task, Syracuse asks about the song she was singing earlier, but the woman doesn’t remember where she’d heard it. When asked if she remembers her name now, the lady tells him to call her Ondine, which is from a story of a girl who came from the water.
As the day goes on, the two find that Syracuse’s lobster traps are all empty. Later, Ondine sings while the fisherman hauls another trap, and to his surprise, a lobster is finally there. Thinking that her song is connected to the sudden good luck, the fisherman has her sing again while he’s lowering another trap.
When he pulls it out, he gains two more catches, convincing him that Ondine brings him luck. Later, Syracuse sells plenty of lobsters in the market. With the money, he shops for clothes but sneakily steals some when the saleslady is busy.
He then picks up Annie from school, who insists on racing him home in her motorized wheelchair. On their way, he continues his story, adding that the fisherman who found the mysterious woman gets more fish when she sings. After he leads her back to her home, Syracuse continues driving, unaware that his daughter is following him, curious about his story.
He brings the new clothes and some food to Ondine. The woman kisses him on the cheek to thank him, but the man doesn’t react. Instead, he wonders how long she plans to stay.
The woman thinks that’s up to him, and he responds that she can stay there forever. Syracuse shares that he’s been telling his daughter about her, but as a fairytale. This makes the woman smile before he leaves.
After the man leaves, Annie pokes her head from behind the bushes, curious about what her father is hiding. She then heads to the library, where she borrows books about selkies. Meanwhile, Syracuse goes to the church to meet the Priest.
Given that there are no support groups in their town, the man treats his confessions as his sobriety program. He shares that he had a dream of being at a funeral, and he’s panicking because he’s back with Maura. Unlike him, his ex-wife hasn’t stopped drinking, which makes him worry about Annie.
The Priest suggests seeking help from a counselor, but Syracuse refuses because his fears are a secret. He then hesitantly admits that he stole some women’s clothes. He defends that he was embarrassed about being seen buying them, and he did it for the lady he fished out of the water.
When asked, Syracuse refuses to tell the Priest where she is, so the holy man just encourages him to keep him updated on his developments. The following day, Annie heads to the caravan and finds Ondine swimming in the water, thinking that this confirms her father’s story as real. Hearing this, Ondine discovers that she’s Syracuse’s daughter.
The girl suddenly asks the woman if she has magic powers, like healing her from kidney failure. Ondine doesn’t answer, so Annie asks her more questions based on the books she read. Unsure of what to say, the woman invites her into the caravan, but Annie thinks she’ll put a hex on her if she does.
She then wonders if being underwater is better since she’s sick often. Ondine continues dodging her questions, but the girl is persistent in getting to know her, offering them to become friends. This piques the woman’s curiosity, so she admits that she feels different when she’s in the water.
Annie then asks about her seal coat, but Ondine gets confused. The girl explains that a selkie loses her seal coat when she gets on land and can’t return until she finds it. If she finds it, she can bury it on land so she can stay for seven years and find happiness with a landman.
Having enjoyed her company, Annie kisses her on the cheek before she leaves. Meanwhile, Syracuse goes to the library to borrow books on selkies, but the librarian reveals that his daughter just borrowed them. On her way home, a group of kids teases Annie about her wheelchair.
When one girl asks to ride it, Annie hesitantly allows her, but the kid tries to take it on water. This breaks her wheelchair, forcing Annie to push it back home. While Alex fixes her wheelchair, she asks what he knows about selkies.
The man claims that it’s a Scottish legend, though Annie comments that Ondine didn’t speak like a Scot. Later, Syracuse and Ondine go fishing. He assigns her to steer, but when another boat passes by, the woman quickly hides.
Still not wanting anyone to see her, Ondine starts steering using her feet, which makes the man curious. She sings, and suddenly, Syracuse’s net gets a big catch. To his surprise, salmon were also in his net, which doesn’t usually get caught this way.
However, as he’s collecting the fish, the Fisheries board patrol heads to his boat, so he warns Ondine. Soon, the patrollers come aboard and notice that Syracuse has caught salmon. Suspicious, they investigate his equipment, but this leads them to discover Ondine.
The two claim that everything is normal, so the patrollers eventually leave. Given that the patrollers saw Ondine, Syracuse is relieved that he’s not just imagining her. The woman worries that the patrollers will talk about her, though the fisherman isn’t bothered since he’s been the topic of rumors before.
Since people will know about Ondine anyway, the two head to the harbor together, catching the attention of other fishermen. After selling the fishes, Ondine joins him in town to buy her clothes. This leads them to bump into Annie, who reveals that they’ve already met.
The girl joins them and helps Ondine choose clothes. However, Syracuse’s lady companion becomes the hot topic of the town. On another day, Annie visits Ondine alone.
Upon learning that the girl can’t swim, Ondine offers to teach her. However, while they’re in the water, Ondine finds something bundled in seaweed. Thinking it’s her seal coat, Annie encourages her to bury it so she can stay with them for seven years.
With that, the two bury it in the abandoned greenhouse near the caravan. They then go with Syracuse to the regatta. On their way, Annie keeps listing myths about a selkie, who can grant wishes and stay with them unless she has a selkie husband.
However, Ondine insists that she isn’t a selkie, nor does she have a husband. Elsewhere, a mysterious man notices a seal in the water and kicks a fish to feed it. While joining the festivities, Annie dares Ondine to prove that she isn’t a selkie.
With that, she drives her wheelchair to the edge and falls into the water. Immediately, Annie dives in to save her while Syracuse hurries to them. When her father gets her on a boat, Annie claims that her brakes broke.
However, she adds that Ondine managed to save her because she breathes underwater. After dropping Annie back at Maura’s house, Ondine admits to Syracuse that his daughter fell on purpose to test her. She then asks why people call him Circus, so the man shares that he was a clown when he was a drunk.
He stopped drinking when he found Annie in danger while Maura was passed out. This convinced him that at least one of them should be sober to keep their daughter safe. However, it ended their marriage.
Given that their laws don’t award custody to fishermen who were away often, Annie ended up with Maura. As Ondine comforts him, the two become drawn to each other, leading to a passionate evening. Meanwhile, Maura asks her daughter about Ondine, adding that someone was looking for the woman.
This bothers Annie, who later dreams about the mysterious man coming out of the water. The following day, Syracuse attends a confession, though the Priest has already seen Ondine. He assumes that the fisherman slept with the woman, which Syracuse confirms.
The man explains that he’s telling this to the Priest since keeping secrets can drive one mad. With that, he admits that Ondine brings him luck, but he’s afraid that something is about to happen, and he’s not sure if it’ll be wonderful or terrible. Upon leaving the church, the mysterious man approaches Syracuse, but he ignores him.
He then takes Annie to her dialysis appointment, though he heard from Maura that she was upset last night. Annie disregards it as her imagination, noting that she has time to imagine while waiting for her blood to be cleaned. When they return to Maura’s place, they find that no one’s home.
As the two search for Maura in town, another car drives to Ondine’s home, surprising the woman. She quickly hides in the greenhouse as the mysterious man searches her home. Syracuse finds Maura and Alex at the pub, refusing to give him their house keys since they think Annie will be fine hanging out with them.
His daughter insists that she’ll be okay, so the man has no choice but to leave. He goes to the caravan but finds it ransacked. Thankfully, he finds the woman by the stream, sharing that she thinks her selkie husband is the mysterious man.
Recalling Annie’s claim that Selkies grant wishes, Syracuse suggests that Ondine can wish the man away. She refuses since her wish is for Annie not to be sick anymore. The man agrees to her wish but also wishes for Ondine to stay with them.
As they talk, the mysterious man is driving back into town. Coincidentally, a drunk Maura is driving home with Alex and Annie. This leads to the two vehicles colliding, which instantly kills Alex.
Soon, Syracuse and Ondine discover the accident, much to their horror. Hours later, Annie wakes up in the hospital, but the doctors take her for her operation. While Syracuse and Ondine follow, they pass by the mysterious man, who yells for the woman upon seeing her.
Seeing him brings Ondine’s memories back, leaving her frozen in the hallway. Meanwhile, a doctor pulls Syracuse aside, revealing that Alex was registered as a donor and his kidneys are a match for Annie. Because of this, they immediately perform a transplant to save the girl’s life.
Later, Ondine finds the man in the chapel, who’s surprised that she’s speaking the people’s language. Resentful of the man, she tells him to go home, but he insists that he can’t since the police want to talk to him about the accident. As he draws closer to her, Ondine storms off.
Days later, Alex’s funeral is held as an injured Maura scatters his ashes. Syracuse sympathizes with his ex-wife, feeling guilty over what happened. However, Maura assures him that he wasn’t at fault.
She then tells him to take Annie to his home since she can’t handle watching over her while she’s recovering too. However, Maura insists that Ondine can’t be with her daughter. They then head to Alex’s wake at the pub, where Maura manipulates Syracuse into drinking.
She also tells him to get rid of Ondine, suggesting she brings him good luck first, then bad luck. That evening, Syracuse drunkenly heads to his boat, where Ondine has been hiding from the mysterious man. With his intoxicated mind, he decides to take Ondine to her home.
He drives further into the sea, questioning the woman about her husband. However, she clarifies that the man isn’t her husband. Still, he insists that she’s better off at the sea.
They head to a lighthouse, where the man leaves Ondine, convinced that their fairy tale has to end to stop further tragedies. The following day, the Priest finds a hungover Syracuse on a tree. As he sobers up, the man realizes his mistake of accepting good luck.
However, the Priest tells him that misery is just easy while happiness takes work. Later, Syracuse finally takes Annie to his home. She asks about Ondine, so her father claims that she went on a sea business.
However, Annie is sure that she’ll be back because she left something, which she refuses to tell her father. The following day, Annie is watching TV when Syracuse hears Ondine’s song from a foreign singer. As he realizes that the woman might not be mythical, his daughter encourages him to find her, so Syracuse heads back to the lighthouse.
He spots the woman on the shore near the lighthouse, claiming to have joined the seals basking in the sun. She asks what made him return, so he explains that he heard her song on the TV. The fisherman now wants the truth, so Ondine finally reveals that she was a mule from Romania.
She was on a boat to deliver contraband, but the Coast Guards found them. The mysterious man, Vladic, was her handler, and he forced her to escape with their supply since he couldn’t swim. However, the land was too far, so Ondine discarded the bag of supplies and let herself sink into the water.
This was when Syracuse found her. As the man takes her back to town, she reveals that her real name is Joanna. They return to Syracuse’s home, only to find Vladic with Annie.
Immediately, the father beats the man, but his thug arrives. With a gun aimed at Syracuse, the men interrogate Joanna about the supply she took. Thinking that they mean her seal coat, Annie begs the woman not to tell them where it is, but this makes the woman realize that the bundle she found was the bag of supplies after all.
With that, she takes them to the greenhouse, only to find the bag missing. Maddened, Vladic accuses Annie of moving it, so Joanna begs the child to tell them where it is, promising to stay with them if she does. Finally, Annie reveals that she hid it in the lobster trap, so the men fish it out.
As they do, the child whispers to Joanna that her “husband” doesn’t seem to be a selkie. Recalling that her handler can’t swim, the woman pulls on the rope they’re standing on, tripping them and sending them into the water, where Vladic drowns. Soon, the police arrive and arrest his thug.
Syracuse visits the Priest days later, sharing that Joanna is awaiting deportation. This, however, can be avoided through marriage. Next, Annie visits the Priest, confessing that she lied about throwing the seal coat into the lobster trap since she actually wants Joanna to stay with them.
She reveals that her father is marrying her next week, so she asks the Priest to officiate the wedding. Soon, Syracuse and Joanna get married on the same boat where they met, thus living happily ever after.
