In the Bering Strait during a violent storm, three fishermen are hauling in a large net of fish when they scream that something big is caught inside. They release the net, dropping its contents on the boat. They notice it moving when it lashes out at them. Grabbing weapons, they corner it into a large bin as it injures their friend Chris. As Chris' crew-mates bring him inside and try to treat him, the captain reports the incident, saying he doesn't know what hit him. Xander, along with his remaining crewmates, begin to hear mysterious singing and go up onto the deck to investigate their catch. Just as he opens the lid, the spotlight of a helicopter surprises them as Naval SEALs drop down on ropes. The SEAL leader is eager to open the door, but the captain insists they tend to his injured worker. Chris is strapped to a stretcher and taken away in the helicopter, and the leader opens the lid, looking at the specimen inside it. A shooter beside him subdues what's inside, and, in a large metal box, carry it away in the night. And something in the water is witness to it all.
On a sunny day in Bristol Cove, their annual "Mermaid Days" Festival in full swing. Among the festivities is a children's play retelling of a legend where a captain named Charles H. Pownall, the town founder, fell in love with a mermaid, only for the mermaid to break his heart. As it ends, Ted Pownall appears, telling the audience that was his great-great-great grandfather as he introduces his wife Elaine and sons Doug and Ben. However, Ben proves to be absent. Nonetheless, his father unveils a statue of Captain Pownall. In the midst of the crowd cheering, he asks his wife where Ben is.
Ben is later seen parking a boat by the docks with Maddie, rescuing a sickly sea lion who was 30 miles outside her usual range. As they head out, Ben says it was good they went out, with Maddie adding against his dad's wishes. She also says he doesn't agree with Ben being with her. Ben says if he did everything his dad told him, he'd be Doug. He asks her out, but Maddie says she needs to take care of her dad. They eventually agree to meet up later as they kiss.
At a bar called the Anchor, Ben meets up with Xander, who says he has something to tell him. His other crewmate is upset as they thought they'll keep it to themselves, but Xander insists Ben can help them. He tells Ben of the unusual encounter plus the military-like response. He also tells him of Chris' disappearance. Showing Ben the security footage of the boat, he's convinced it's a mermaid, but Ben is skeptical and thinks it could be something else.
At a military base, an official is briefing an admiral about reports of possible mermaids sightings around the world. He brings up the incident in the Bering Strait. The admiral asks if he thinks it's the real deal, to which the official tells him to judge for himself. They walk through a lab, where a paralyzed Donna is trapped in a tank.
Elaine visits Ben, telling him his father is very angry with him. She says he's angry about a lot of things, like her buying $600 shoes despite her being in a wheelchair. Elaine comments on the latest insult Ted threw at her - "bitch on wheels", revealing a history of abuse. She tells him it's okay as long as it's behind closed doors. She elaborates and says they have to put on a show for the town, and how he was supposed to be at the festival with them. Ben isn't having it - he doesn't want to be included and has other stuff to worry about. Elaine tells him she knows about him and Maddie from Doug, and says he always had a thing for the wild girls. Ben says he has some things to do and bids his mother goodbye, closing the door and revealing that Maddie is inside and heard everything. Maddie says she and his mother might actually hit it off if they met, and Ben says she's right - Maddie is the exact kind of girl she'll want for him - beautiful, smart funny and passionate as he kisses up her arm and they kiss.
At a bonfire near the shore, Maddie notes that she doesn't remember Jerry being such a "burner" in high school. Ben remarks that the burners were more so her crowd. He then notices Xander all by himself and takes this opportunity to talk to him after their disagreement at the Anchor. He passes a woman scolding a boy as he enters the water. Xander isn't upset with Ben as he should've known better than to expect him to believe that mermaids exist. Ben doesn't come out with them on the boat anymore, so he wasn't there to see it himself. Nonetheless, they took Chris. Ben argues that he was likely taken to a military hospital and that his disappearance isn't due to a cover-up that Xander believes to be taking place. Despite all this, Xander stands firm on his belief that they caught a mermaid. And with Ben admitting that 95% of the oceans remain unexplored, who was he to say otherwise. In order to make Ben a believer, Xander plots to catch another mermaid. Meanwhile, the appearance of a shark's decapitated head terrifies the boy in the water. Xander suspects that it's the doing of a mermaid while Ben and Maddie have not the slightest clue as to what could've ripped a shark's head off.
At the research center, Maddie and Ben examine the shark's head. The bite radius was far too small for it to have been done by an orca whale. And it certainly wasn't done by another shark. Maddie proposes another explanation; maybe it got caught in a boat prop and a sea lion bit the carcass, but Ben begins to suspect that there might be a new predator in the ocean, one they haven't seen before.
After Ben leaves the research center, a mysterious girl steps out of the woods completely naked. She stares into the headlights of the car as Ben comes to a screeching halt. Ben follows the girl as she stumbles across the road, asking if she is okay but to no response. The stumbling girl doesn't make it far before passing out. Ben wraps her in his coat and puts her in his car. He then calls Dr. Abbott and arranges for the girl to be checked out at his house. Upon arriving at the boathouse, after dressing the mysterious girl, he offers her something to drink as she wakes up. The girl doesn't speak and exhibits odd behavior. In spite of this, Ben offers to help her. Still, she doesn't talk. However, she does sing to him, emitting a captivating sound that nearly puts Ben in a trance. It is then that Dr. Abbott arrives. Ben invites him in, but warns the doctor that the girl is a bit strange. Unfortunately, by the time they return, the mysterious girl is gone.
As he wakes up, Ben still dreams of Ryn's song. And Ryn, having found shelter, wakes in an abandoned boat in the wilderness. She tests out her feet once more as she spots a rat. Deciding the rat will be her next meal, Ryn steals a hoodie from a drying rack and heads into town. Exploring her surroundings, she encounters Helen Hawkins in front of her shop. Helen hears the echoes of Ryn's soothing siren song, and seemingly recognizes her as what she truly is. Ben, trying to locate Ryn in his spot, finds her with Helen. Ryn, however, is bumped away from Helen and disappears again. Ben, having caught up to the pair, asks Helen where the girl is. Helen responds that she didn't see anyone and runs inside, leaving a confused Ben behind.
Ryn makes her way to the docks, and finds the North Star - the boat where Donna was taken to. She boards the ship and kneels over the net, where she experiences the flashback of her and Donna hunting fish and Donna getting trapped in the fishing net.
At the Bishop residence, Sheriff Dale Bishop asks his daughter if she's heard from Chris. He tells her his family hasn't heard from him since he was taken away by the military chopper, and that they've got Sheriff Bishop calling every base in Alaska to look for him. They hold their hands for a blessing at the dinner table, and Sheriff Bishop prays Maddie's mother Susan finds guidance since she took off eight months ago.
The next morning in a trailer park, Ryn injures her bare foot on a spot of broken glass, finding a bare of yellow rubber boots. She notices a toy helicopter, reminding her of the one where Donna was taken. She sees a little boy playing and watching cartoons on the television. The television introduces a new character named Ryn, and the girl announces her first words to be "I am Ryn." The little boy hears her and says hello, but scares her off. She later encounters Donnie, who greets her. Ryn tests out her new phrase, and shows him the toy helicopter. Donnie, sensing Ryn's incomprehensibility, motions a helicopter swoosh as she sees his car. Recognizing it as a mode of transportation, she opens the door and gets it as Donnie assumes she wants a ride. In the car, Ryn motions to the toy, indicating she wants to be taken to the helicopter. Donnie misinterprets it as a childish act, and he turns to park the car in a secluded space. He takes out a bottle of alcohol, and believes Ryn to be nothing more than a little girl running away. He takes her hand and forces her to touch him, and begins to force himself on her. Ryn viciously attacks back, and throws Donnie's body through the windshield. She steps out, and sees her scales return back to her skin.
Ryn makes her way to the Bristol Cove Marine Research Center, and joins a class of schoolchildren on a tour of the faculty with Maddie acting as their guide. Inside, Maddie shows them a shake of fish and nutrients that tempts Ryn, who drinks it when the group heads outside to see some sea lions. However, Ryn's presence causes the sea lions to become quite aggressive. The group backs away, a little girl, who noticed Ryn, points out that she is responsible as Ben comes. Threatened and scared, Ryn retreats inside but Ben promises he wants to help. Ryn, clearly ill and breathing roughly, coughs and allows Ben to look at her scaled arm. He tells her about the song she sang to him and how he can't get it out of his head. After Maddie returns and says she got the situation outside under control, Ben informs her he thinks Ryn doesn't speak English but requires Doctor Abbott. Maddie leaves to return to her class while Ben trails after her to call the doctor and get medication.
At night, Ryn, whose scales are returning at a faster rate and has continued trouble breathing, takes off her boots and collapses on the floor. Crawling, she makes her way out of the shed office to the water outside to complete her transformation from human to mermaid. Ben, hearing a commotion, runs back into the office and sees the security footage underwater, which catches Ryn's face. He storms outside and dives into the water, flashlight in hand. He spots Ryn in mermaid form, but she quickly turns back and charges at him. Ben tries to swim away but she strikes him, thus ensuring a battle. Ryn slashes at him but Ben hits her and momentarily subdues her. He swims back to the surface and tries to reach the dock, but Ryn returns to catch his legs. Able to reach a pole, he thrusts it to her, and uses the pole to warn her back. However, she is eventually knocked unconscious as Ben makes it to safety.
Dr. Abbott finds him and wakes Ben up. Convinced a sea lion attacked him, he watches as Ben awkwardly stands up and looks out the sea, asking where Ryn is. Dr. Abbott assumes it's Ben's mystery date and asks him if there's something he needs to say.
Ben runs to Helen's shop, frantically asking her to let him in and that he knows she saw and knows about Ryn. Helen asks him what he saw, and he tells her he saw Ryn transform in the water. He realizes all the mermaid tales Helen told in his youth were true and asks her why she isn't spreading the truth. Helen, noticing the scars on his neck, responds that mermaids are predators and view humans as their prey. She informs him of his true ancestry - how Charles H. Pownall slaughtered mermaids in cold-blooded genocide and Ben is to follow in his legacy. Ben runs out, but not before he steals and reads a book detailing the true history behind the mermaid genocide.
At the Bishop's, Maddie's made several calls to Ben, all of which have gone unanswered. Dale assures her that it's nothing and that Ben's most likely just busy. He then receives a call that a body was found, having been thrown out of a car.
At the North Star, Xander hands his father, Sean, the captain, a harpoon as he boards. He notices Ben, who wants to join him. Happy to have his friend help, Xander helps him up. Just like old times, Xander remarks. Both of them agree to try and catch one, intent on the military to show up and lead them to Chris. Chris is then shown to be in a white medical room at the military base, attended by a nurse and guarded by two soldiers.
Back at the boat, the captain spots something in the radar, something big and moving fast. All three men head to the deck, with the captain armed and staring into the sea. He spots a disturbance in the waters, and shoots the harpoon as the sea creature emerges for a retaliatory assault.
Special Guest Star
- The pilot episode was filmed in October 2016, in BC, Canada.
- One of the primary settings during production for the pilot episode was Steveston, but filming also took place in Deep Cove and Port Moody, all in Canada.
- This episode consists of one particular VFX sequence that takes place under water with the mermaids as they hunt. The mermaid tail effects for this scene was done by Pixomondo, the same visual effects company known for designing the dragons in Game of Thrones.
- The scene in which the boy is lurked in the water references the classic horror Jaws, though here the shark becomes the prey.
Ben: "She...changed in the water. Like this. When we kids, we'd come in here and you'd tell us stories about the mermaids. We told that they just tall tales, not to believe you, but they weren't made up, were they? They were true. i don't get it! You want people to know the truth. Well, it's here! It's happening!"
Helen: "She do that to you? In their natural state in the water, they see you as prey. Their instinct is to kill. Humans never understood that. It caused a lot of misery."
Ben: "What do you mean?"
Helen: "Your family's history in this town is bloodier than you know. Your ancestor lost his mind. Obsessed. He and his fellow ship-mates slaughtered those beautiful creatures in cold blood. Genocide- That's your legacy. Why not ask your family about that?"
- Rabbit by Tanya Tagaq
- It's Moving
- Bristol Cove Morning
- The Run Up by Make It
- Lonesome City by The Black Canyon Gang
- Twenty-Four Seven by Kasabian
- Cold Feet by Fink
- Angel of the Morning by Juice Newton
- In the Rain by Flagship
- Vulture — "Freeform Orders a ‘Thrilling,’ ‘Complex,’ and ‘Scary’ Pilot About Mermaids" (July 25, 2016)
- SpoilerTV — "Final Adjusted TV Ratings for Thursday 29th March 2018" (March 30, 2018)
- SpoilerTV — Freeform's March 2018 Programming Press Release (February 23, 2018)
- What's Filming—"Siren Season 1 Starts Filming in Vancouver" (August 2, 2017)
- YouTube Comic Con — "Siren New York Comic Con Panel | Freeform" (October 29, 2017)