- This marks the final appearance of Donna and Aldon Decker in the show.
- Helen and Ben are revealed be distant cousins, as Helen is the last living descendant of the daughter of Charles Pownall (Ben's paternal great-great-great-great grandfather) and his mermaid lover; being one-eighth mermaid through her great-grandmother. However, Helen lacks the agonizing aquatic ability to transform into her mermaid form, having skipped her generation.
- Donna perishes from her wounds and is laid to rest in peace with fellow mermaids who were slaughtered while in human form centuries ago.
|“||I didn't know my song would do this.||”|
|— Ryn to Helen and Maddie about the captivating and irresistible melodic Siren Song|
|“||We used to make decisions together. But I see you talking about Ryn. Even bringing Decker in.||”|
|— A hurt Maddie chastising Ben|
|“||She sang to escape from you. Not because she loves you.||”|
|— Ryn to Decker about her sister Donna|
|“||I sense she is one of us.||”|
|— Ryn to Maddie about Helen's true nature as 1/8th mermaid and 7/8th human from her great-grandmother.|
|“||Great love, but to others, it can be...dangerous. Obsession.||”|
|— Helen to Maddie about the mermaids' captivating melodious and irresistible siren song.|
- Cry No More by Vaults
- Hurricane by Flagship
- Minimum by Charlie Cunningham
- Mercy & Lightning by John Mark McMillan
- Open Passageways by All Them Witches