Madison tries to bring her sister to a human party, in an attempt to prove that people aren't dangerous. Meanwhile, the evil trio attempts their first abduction.
In order to prove to her sister that not all humans are bad, Madison tries to convince the party-goers to help with a beach cleanup. Valerie ends up kidnapped by Jed, Astrid, and Stanley.
Stanley invites Madison and Valerie to his house for a Christmas party. It's their first experience with a human holiday, but the party goes horribly wrong when Stanley's girlfriend arrives and the mermaids become convinced she's an evil crab person in disguise.
While hiking with Nat, Stanley recalls how, as a child, he was saved by a kind mermaid, which sparked a strong love for merpeople in him for years to come.