Bristol Cove mourns a loss causing Ryn to experience a new human emotion.

Donna comes ashore with two other members of her colony to bring Ryn back home. When mermaids once again begin wreaking havoc throughout the town, Dale tries to put an end to it once and for all.

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.

Ryn returns to land to explore human motherhood. Maddie and Robb come across a gruesome discovery. Ben experiences mysterious side effects and Ted confronts Helen.