The military gives Maddie a psychological evaluation and she storms out.
Helen finds a newspaper article about her family's cabin which claims its destruction was arson and that her family was in the cabin when it burned down.
Ryn brings a mermaid back to heal Ben and Maddie, but she says the song is too strong. She tells them about a secret place in the ocean where Ben and Maddie can be healed, but it's too deep for humans.
Xander and Nicole decide to give their relationship another shot.
The military allows Ben, Maddie, and Ryn to use a submarine as long as the expedition is fully documented.
Maddie apologizes to Xander for almost kissing him.
Beth tells Rick she's not sure if they can trust Helen. Rick tells her that full-blooded mermaids exist and were in Bristol Cove.
Levi comes back to land and Xander and Calvin try to convince him to go back in the water.
Ben, Maddie, and Ryn descend into the ocean.
Helen goes to John to try and get answers about her parents. He tells her that her father was human and her mother was a descendant of the mermaids, which made their relationship forbidden.
A group of men attacks Xander and Calvin, but Levi helps them.
Ben disconnects the camera so the military can't watch them. Their sub sinks into the sand. They reach the place where Ryn was born and see Ryn's family.
Ben, Maddie, and Ryn reach the healing place. They go back to the surface and Nicole scolds them for the radio silence.
Helen accuses Beth of knowing who killed her parents. Beth passes Levi on the sidewalk.
New brain scans reveal that whatever Ben and Maddie were exposed to in the ocean helped the effects of Ryn's song.
Ian, the reporter, asks Calvin if he can see the video he had told him about before, but Calvin tells him it was just a sea lion.
Xander comes over to see Nicole, and while he's in the shower she watches a live video feed of Ben, Maddie, and Ryn.