A costal town known for its legend of once being home to mermaids is turned upside down when a mysterious girl appears and begins wreaking havoc.
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. Helen and the hybrids help restore order. Ted struggles to accept Ben's reality.Watch Now:AmazoniTunes
Mermaids and humans join forces in a radical plan to stop the oil company, but their efforts have a devastating effect. And facing an uncertain future, Ben, Maddie and Ryn come together for a romantic farewell.Watch Now:AmazoniTunes
Ryn discovers a refuge of injured mermaids that 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.
Dale copes with the fallout from Maddie and Ryn’s encounter with the man from Susan’s past, while Katrina continues to persuade the rest of the mermaid pack to get on her side, even if that means brute force against both mermaids and humans.
Tensions are rising following a shocking discovery. And living in a tank rather than the ocean is starting to have an adverse effect on many of the mermaids. Hoping to save her kind, and help her human circle, Ryn makes a deal with a complicated ally.
Tia unleashes a deadly attack on Bristol Cove. Ryn, Ben and Maddie race against time to find a cure for Xander's mysterious illness, while anticipating Tia's next move. Baby Hope returns to land to reconnect with Ryn.
Ryn continues to try to teach the other mermaids to be more human in order to better assimilate, but some are starting to resist her, causing Ryn to wonder if she herself is becoming too human. Maddie finds herself in a dangerous situation trying to help her mom. Meanwhile, Ben and Xander reconcile in order to work together to get the mermaid pack back into the water.
Ryn, Ben, and Maddie must recruit new allies in the fight against Tia. Helen seeks answers when she's haunted by Donna's spirit. Tia obtains dangerous weapons she plans to use in her fight. Xander struggles to make amends with Annie.
Ryn seeks help only to learn the secret existence of her unborn child. Ben sets out on a dangerous path to help his mother. Xander tries to establish himself in his new career. Helen consults with Eliza to help contact Sarge.
Ben, Maddie and the other humans deal with the fallout from the attack on the oil rig, while the mermaids reacclimate to their ocean home. Ryn comes back to land to follow through on an agreement she made with the military, despite not knowing what their ultimate goals are.
Ben and Maddie help Ryn guide her surrogate though a life-threatening delivery. Helen and Xander deliver a hybrid corpse to Beth at The Ranch. Xander faces danger on the high seas during a ride-along with the Bristol Cove water patrol.Watch Now:AmazoniTunes
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.Watch Now:AmazoniTunes
Ryn fights to maintain leadership of the pack when her loyalties are questioned over her friendship with Ben and Maddie. Ben interferes in a mermaid ritual and Helen discovers more about her family lineage.Watch Now:AmazoniTunes
Ryn, Ben and Maddie must protect Bristol Cove from Tia's army. Ben's injections are producing unexpected results, which alarms both him and the others. Xander juggles best man duties at Calvin's wedding while also helping Helen.
Ben and Xander are left dealing with a shocking discovery about Chris and his connection to the military. Meanwhile, Helen and Maddie reluctantly seek help from the hybrids as the threat of extinction looms over the mermaids. Ryn encounters the journalist who continues to chase his theories on mermaids to increasingly desperate ends.
With Elaine Pownall’s health worsening, she seeks treatment from the military’s medical trial using mermaid cells, but the procedure doesn’t come without side effects to the mermaids. Helen and Rick learn more about the hybrid status, their history in Bristol Cove, and discover they are far less alone than Helen once believed.
Maddie and Ben contend with how to help Ryn knowing that in order to help Elaine get better, they will need to continue the procedures on Ryn. When one of the group gets sirened, there is more drive than ever to get to the bottom of how the siren song really works—further piquing the interest of the military in how Ryn can be of use to them.