On a dock in Haven, a group of children sing a somber song on a dock. All seems well until they abruptly throw one of their own into the water with a cinder block tied to his feet. Soon, a man with the tattoo that Duke is deathly afraid of interrupts the kids for dinner.
When that same man shows up washed up on the shore of Benny's Cove with a suicide note in his pocket, Audrey and Nathan stat trying to piece together what happened. Following up on a picture in the dead man's pocket, they find out that the man's name was Leath and that he was part of the mysterious Glendower family. They also discover that Daniel, Leath's son, is missing too.
Audrey and Nathan try to get Daniel back from the Glendower clan, but the family refuses to give him up. Is something sinister happening at this Glendower compound? Meanwhile, Mary, Leath's former girlfriend, enlists the aid of Reverend Dricscol to take Daniel back by force. Nathan is barely able to talk them out of it, especially since Reverend Driscol blames the Glendowers for his wife's disappearance years ago.
When Audrey and Nathan sneak into the Glendower camp to have a look around, they find that the Glendowers are keeping Daniel submerged in a bathtub full of water! When they try to take Daniel out of the tub, however, it become apparent that he's more comfortable in the water. It turns out that Daniel, like all of the Glendower men, is transitioning into period of time when he can only breathe water.
When Audrey deduces that the suicide note found of Leath's body was actually written by Penny, Cole Glendower's wife, she and Nathan eventually discover an even bigger secret-that Penny is, in fact, Reverend Driscol's missing wife. All these years, she's pretended to be dead in order to marry Cole Glendower.
They don't have much time to explore this fact before they realize that the boys have been kidnapped. Leth's girlfriend Mary has taken the boys to prevent the Glendowers from harming them in any way. With all of the boys gasping to breathe and about to die, Audrey and Nathan must rely on an unexpected ally to save their lives-Reverend Driscol himself.
In the process of saving the boy's lives by talking some sense into Mary, Driscol comes face to face with the wife he presumed dead-a sobering experience for everyone involved. Mary, on the other hand, learns to accept the Glendower "trouble" and let Daniel go out to sea.
Cole Glendower, it turns out, killed Leath, because Leath threatened to tell Reverend Driscol that his wife was still alive. Nathan can't put Cole in prison because of Cole's dependence on water to live, but he promises to keep a close eye on him.
Meanwhile, Duke's wife Evi has been manipulating Duke all along, moving him closer to Reverend Driscol for reasons unknown.