Siren

The coastal town of Bristol Cove, historically recognized as a home to mermaids, experiences significant disruption with the arrival of a mysterious girl.

Ben and his crew of *The North Star* discover a device emitting an unusual sound. At the same time, Ryn takes shelter in the home of a local folklore expert.

Dale and the local police begin to suspect Ryn in their investigation, while Xander and Calvin intensify their search for Chris after finding the nurse who works at the military bunker.

When the military facility enters high alert, Chris manages to escape, but he is not the only one to do so.

Ben begins to investigate some suspicious overfishing, while Decker intensifies his efforts to find his escaped mermaid, revealing the true extent of his influence.

At Ben and Maddie's attendance of his mother's fundraising gala, an unexpected guest arrives and proposes a solution to the overfishing endangering the mermaids in Bristol Cove.

When Ryn is taken in for questioning, Maddie rushes to her rescue. At the same time, Ben and Xander return to the deep sea in search of answers, only to be met by an uninvited guest.

Bristol Cove is grieving the loss of a member of its community, an event that prompts Ryn to encounter a previously unknown human emotion.

Donna arrives on land with two other members of her colony to retrieve Ryn and bring her back home. As the mermaids continue to cause chaos in the town, Dale attempts to find a permanent solution to stop their disruptions.

In the season finale, the enchanting siren song takes hold of Ben and Decker. Meanwhile, Dale must answer for the escalating crime in Bristol Cove.

As more mermaids arrive at Bristol Cove, the risk of being discovered by humans grows. Following his experience with the siren song, Ben struggles to deal with its lingering effects. Maddie's mother comes back to town and makes an effort to reconnect with her. At the same time, Ryn works to adjust to living on land.

Ben, Maddie, and Ryn work urgently to conceal the newly arrived mermaid pack from the rest of the town. However, the mermaids' rapid deterioration on land forces the trio to find a way to return them to the sea without being noticed, particularly during the town's Mermaid Beauty Contest. Meanwhile, Elaine becomes increasingly suspicious of Helen and her potential ties to their family.

Ryn struggles to hold onto her position as leader of the mermaid pack as the others begin to doubt her loyalty. Ben's interference in a mermaid ritual creates tension between him and Ryn, while Helen uncovers new details about her family's history.

Ryn realizes they need to find an alternative solution for housing the mermaids, as keeping them hidden becomes more challenging. Ben takes on a mentoring role for Levi, helping him understand how men behave on land, while Maddie continues to deal with the difficulties of her mother's return to her life.

Ryn continues her efforts to teach the other mermaids how to act more human in hopes of improving their ability to assimilate into human society, but some of them begin to resist her guidance, leading Ryn to question whether she is becoming too human herself. At the same time, Maddie faces a dangerous situation as she attempts to assist her mother. In parallel, Ben and Xander work toward reconciliation in order to collaborate on a plan to return the mermaid pack to the ocean.

Dale deals with the consequences of Maddie and Ryn's encounter with the man from Susan's past, while Katrina continues to push the rest of the mermaid pack to support her, even resorting to brute force against both mermaids and humans.

Tensions escalate after a shocking discovery is made. The mermaids, who are living in tanks rather than the ocean, begin to experience negative effects. Determined to save her kind and assist her human companions, Ryn forms an alliance with a complex and challenging ally.

In a bold effort to halt an oil company, mermaids and humans unite, but their actions lead to unintended and devastating consequences. As their future becomes uncertain, Ben, Maddie, and Ryn share a final, romantic moment together.

Ben, Maddie, and the other humans manage the aftermath of the attack on the oil rig, while the mermaids adjust to returning to their ocean habitat. Ryn returns to land to fulfill a promise she made to the military, even though she remains unaware of their ultimate intentions.

As Elaine Pownall's health declines, she turns to a military medical trial utilizing mermaid cells for treatment, though the process carries unintended consequences for the mermaids themselves. At the same time, Helen and Rick uncover more about their hybrid identities, their historical ties to Bristol Cove, and the realization that they are not as isolated as Helen previously thought.

Maddie and Ben struggle with how best to assist Ryn, aware that continuing the procedures on her is necessary to help Elaine recover. At the same time, when one of the group is sirened, the urgency to understand how the siren song functions intensifies, further drawing the military's interest in Ryn and what she might be able to offer them.

Ryn returns to the ocean in search of assistance for Ben and Maddie's conditions, only to realize that continuing to travel between land and sea may become increasingly difficult the longer she remains on land. When they discover there may be a special place in Ryn’s homeland that could offer a cure, Ben, Maddie, and Ryn decide to journey beneath the sea together to find it. At the same time, Helen and Ted begin to bond through their shared family histories.

With mermaid mating season underway, Ryn becomes aware that she must return to the sea to assist her colony. The hybrids persuade one of the mermaids to accompany them to a secluded location, prompting Helen and Ben to embark on a search to locate them. A journalist seeks Xander's assistance in uncovering the events of the night of the oil rig disaster, though Xander struggles with uncertainty over where his loyalties should lie and what the consequences of helping might be for his future.

The mating season proved less successful than anticipated, prompting concerns about the mermaids' ability to reproduce on land. To address the colony's needs, Ryn brings a new potential mate ashore, a decision that stirs emotional tensions for Ben and Maddie.

Ben and Xander are forced to confront a startling revelation regarding Chris and his ties to the military. At the same time, Helen and Maddie are compelled to seek reluctant assistance from the hybrids as the mermaids face the looming threat of extinction. Ryn comes across the journalist who continues to pursue his theories on mermaids with growing desperation.

Ben must make a decision with far-reaching consequences for mermaids, hybrids, and humans as the truth about mermaids is revealed.

As an old friend visits Helen, a new mermaid arrives, prompting Ryn to question their motives. Maddie discovers the truth behind Ian's death, while Ben fights for his mother's medical treatments. At the same time, Xander is inspired to take on more responsibility.

When another mysterious death is uncovered in Bristol Cove, Ryn suspects Tia. Maddie befriends a new acquaintance in Seattle. Helen warns the hybrids of trouble. Xander begins training, and Ted revisits the past.

Ryn seeks help only to learn of the secret existence of her unborn child. Ben embarks on a dangerous path to assist his mother, while Xander works to establish himself in his new career. Helen turns to Eliza for help in making contact with Sarge.

Ben and Maddie assist Ryn in guiding her surrogate through a life-threatening delivery. Helen and Xander deliver a hybrid corpse to Beth at The Ranch. Xander encounters danger on the high seas during a ride-along with the Bristol Cove water patrol.

Ryn returns to land to explore the experience of human motherhood. Meanwhile, Maddie and Robb stumble upon a disturbing discovery. Ben begins to experience unexplained side effects, and Ted has a confrontation with Helen.

Ryn discovers a refuge of injured mermaids that have escaped Tia’s violent takeover. Ben and Xander get caught in a battle with Tia’s troops. Maddie feeds Robb half-truths to secure his discretion. Ted explores his family lineage.

Ryn, Ben, and Maddie must find new allies to help in their fight against Tia. Helen is troubled by the spirit of Donna and seeks answers. Tia acquires dangerous weapons intended for use in her campaign. Xander faces the challenge of reconciling with Annie.

Ryn, Ben, and Maddie are tasked with defending Bristol Cove from Tia's advancing army. At the same time, Ben's ongoing injections begin to have unforeseen effects, causing concern for him and the rest of the group. Xander finds himself balancing his responsibilities as best man at Calvin's wedding with his efforts to assist Helen.

Tia launches a deadly assault on Bristol Cove. Ryn, Ben, and Maddie work urgently to find a cure for Xander's mysterious illness while preparing for Tia's next attack. Baby Hope returns to land to reconnect with Ryn.

In an effort to save Hope, Ryn and Ben confront Tia in an undersea battle between the mermaid tribes. Maddie and Robb work to find a cure for Xander, while Helen and the hybrids help restore order. Ted struggles to accept Ben’s reality. Season finale.