Red Locket is the third locket found of the Original Mermaids.
First appeared in the episode "In Too Deep". Rikki was walking through a town center with Zane, when she spotted the locket on a jewelry shop showcase. She recognized that it has the exact same design as Cleo's locket and desperately wanted it. Zane saw how much she wanted it and was planning on getting it for her. But when he ran into Miriam, who he asked if girls like getting jewelry as gifts. Miriam noticed that Zane was planning on getting the locket for Rikki and bought it in order to spite her.
Miriam later got tired of it as her hair kept getting tangled in the chain. She told Zane that she was willing to part with it - in exchange for a kiss on the lips. Without noticing Rikki behind him Zane agreed to kiss Miriam in exchange for the locket. Unfortunately, instead of giving him the locket, Miriam threw the locket into the harbor, where Emma and Zane jumped in to save it. However, Emma's secret was almost discovered in the process. Zane managed to get it back for Rikki, but she risked turning into a mermaid in front of him when he handed her the wet locket. Cleverly, Rikki let the locket slip through her fingers when Zane handed it to her. Before picking it up, she used her power to evaporate the water on the locket. This proves that unlike Julia, Rikki wasn't willing to share her mermaid secret with him just yet.
At the end of the episode, Rikki gave the locket back to Louise Chatham, whom gave it to Rikki because she saw that Rikki was worthy enough to keep it. As she had proven herself to be able to keep her magical identity a secret from Zane.
The locket originally belonged to Julia, who was a mermaid over 50 years ago. Max Hamilton made the lockets; one for each mermaid. Each locket had a different colored stone; Julia's locket has a red stone - possibly a ruby. This could symbolize the ability to heat water. After Julia died, her belongings were sold off as part of a deceased estate. Her locket ended up in the jewelry store where Rikki later saw it.