Ben, Sean and Xander have their sights locked on the sea creature. Just as the captain is about to fire, Ben grabs the harpoon, causing Sean to miss. Ben claims that they need to protect the mermaid, not kill it. However, Xander begs to differ. He wants the mermaid dead and Chris back. They begin to hear a high-pitch scream. Believing that the source of the sound is injured, Ben jumps into the water while Xander and Sean continue to scream his name from aboard the ship. Ben swims under the boat to find a recording device emitting those strange sounds lodged in the propeller. Ben breaks free with the device and brings it on board the ship.
Meanwhile, Back on shore, a trail of disheveled sand leads to the carcass of a mermaid tail. Ryn has returned to land, where she's found comfort in the nearby woods.
Ben believes the device to be a Doppler current profiler, used by Oceanographers to study current patterns. Xander recalls the creature they had locked up in the hold making an eerily similar sound to that coming from the current profiler. Xander suspects that someone put it into the ocean and that it’s somehow related to the creature they captured a few nights prior. Ben then apologies for interfering earlier. He simply feels different about the creatures than Xander and his father but that doesn’t mean Ben doesn’t also want to find Chris. Ben takes the device apart to find a camera and a tracking device inside. Xander wants to set the tracker off in hopes the military will come to lead them to Chris and the mermaid. However, Ben reminds him him what happened the last time the military came. They could all end up disappearing like Chris.
Meanwhile, back on land, a naked Ryn walks idly through a trailer park, sending a mother and her children inside. She spots some clothing on a drying rack and is intrigued by a shirt with an eagle on it. As she put it on, Vicki, the owner, catches Ryn and mistaking her for another junkie, angrily snaps at her. Ryn, spotting a pole behind her feet, hurls it through on the rainfall vents. She scares the owner and runs off. Ryn then breaks into Ben’s house, where a small aquarium catches her attention. As does a photo of Maddie and Ben.
Maddie calls Ben from the research center though he does not answer. Unbeknownst to Maddie, at the doorway stands Ryn. Hearing the growls of the sea lions as she fills the buckets with fish, Maddie turns back to see nothing.
Sheriff Bishop and Deputy Marissa Staub are investigating Donnie Price's crime scene. An officer comments that Donnie had prior charges when Sheriff Bishop notices Donnie's pants are low, assuming that a sexual assault had occurred. Deputy Staub thinks he got what he deserved. The sheriff believes Donnie was with a woman when a third person of "substantial size and strength", snuck up on them. He commands his officers to start searching the area. Peaking inside the car, he notices Ryn's toy helicopter.
In Helen's Antiquities shop, Helen is completing a word puzzle on her desk with a customer shopping inside when Ryn suddenly enters. Helen recognizes who it is, and tells the customer that her shop is closed despite her asking how much is a shirt. She proceeds to change the sign in front of her store from "Open" to "Closed". Ryn, having moved to the left side of the store, watches Helen as she comments that Ryn came back. Helen asks her why she's here, but Ryn hisses in defense. Continuing to look through her surroundings, she finds a terracotta of two mermaids. Saying "I" but struggling to speak, Helen assumes she's trying to say "see" or "look". Pointing at one of the mermaids, she gestures that that's her, Ryn. Helen understands that's her name when Ryn breaks the status in two. Saying "look" to the other mermaid, Helen correctly guesses there's another mermaid.
At the military lab, Aldon Decker tells an assistant that Donna has 30 ccs of spinal fluid and to take six tissue samples. He asks her how the tests are going, to which she responds that they're well. He agrees it's time for the extraction, and Donna, still trapped in her tank, viciously retorts. She calls to him, and he unconsciously faces and begins to approach her, until she turns away.
At home, Ben is finishing his shower when Maddie arrives, saying she got his text. He suddenly embraces her, to which she awkwardly tries to hug back but accidentally touches the scars Ryn left on his neck. She asks him what happened, to which Ben responds that it's not anything she's thinking. Maddie, asking why, receives a reply that it literally couldn't be anything that she's thinking.
Calvin is playing video games when Xander presents him with the Doppler device Ben found attached to the boat. Xander says that Ben thinks they should wait and see who is behind the installation of the device, but Calvin is distrustful of Ben - he never worked hard on the ship with them and coming from the Pownalls, he's not one of them.
Ben is examining the footage of the cameras they have attached to the sea lions, intent on showing Maddie. All Maddie sees are sea lions until Ben finds the footage of Ryn and the battle with her. Maddie is in a state of shock, and as Ben tells her what happened she demands he replay it. Ben tells her it's really happening, and Maddie, stunned, believes Ben when he says it's a mermaid.
Ryn, having been taken in by Helen, picks up a Frozen book but her attention quickly switches to the TV. Helen appears, and a surprised Ryn spins and, using only one hand, roughly grabs Helen's neck. Helen pleads it's her, and Ryn, in a sign of recognization, releases her with an apologetic "Hello, Helen". Ryn picks up the Frozen book again and points at the "Sister" part of the title. Helen concludes that Ryn is looking for her sister. She hands her some clothing, which Ryn roughly takes and dresses. On the prowl once more, Ryn desperately looks for food. Just as she is about to break a jar of olives, Helen stops her and makes Ryn give it back. Helen tells her she knows what she needs, and pleads for her to stay. Helen then locks the shop up before heading out.
Special Guest Star
- The table read began on August 2, 2017.
|“||Charles may not have been the guy we make him out to be. He may had a mental illness, some kind of hysiphernia, constant stream of booze and...Well. He was seeing things. Mermaids?||”|
|— Ted Pownall's skeptical of his great-great-great grandfather's history with a mermaid.|
|“||There's another one? I'll be dammed.||”|
|— Helen to Ryn|
|“||Sisters. Sister. Is that who you're looking for?||”|
|— Helen to Ryn|
|“||It's not about trust. No one can know. These creatures were massacred once. It could happen again.||”|
|“||That sound is your sister?||”|
|— Ben to Ryn|
|“||She's not in there. It's just a recording. Only sound.||”|
|— Helen explaining about the device to Ryn|
|“||There were two of them out there. Her sister's the one who got caught.||”|
|— Maddie realizes Ryn's reason of coming to the surface|
|“||You have no idea what you're dealing with. This will end very badly.||”|
|— Helen to Ben and Maddie|
|“||Whatever you do, don't leave her off on her own and don't make her angry.||”|
|— Helen to Ben and Maddie about Ryn|
- Open Your Eyes by Tyler Blackburn
- Highway Tune by Greta Van Fleet
- Start A Riot by Flint Eastwood
- SpoilerTV — "Final Adjusted TV Ratings for Thursday 29th March 2018" (March 30, 2018)
- SpoilerTV — Freeform's March 2018 Programming Press Release (February 23, 2018)
- Siren Portugal (@SirenPortugal)—Twitter Confirmation (August 2, 2017)
- Rena Owen (@TheRealRenaOwen)—Twitter Confirmation (August 4, 2017)
- What's Filming—"Siren Season 1 Starts filming in Vancouver" (August 2, 2017)