Mer-Mysteries is the seventh episode of Season Four and thirty-third episode overall of She-Ra and the Princesses of Power. It was released on Netflix with the rest of the fourth season on November 5th, 2019.
The heroes suspect a Horde spy in their midst. Mermista attempts to sleuth them out, using tactics from "Mer-Mystery" novels to question nearly everyone in Bright Moon. With counsel from Shadow Weaver, they finally apprehend the culprit.
After a crushing and humiliating defeat in the attempt to retake Dryl, Glimmer calls a meeting of the Princess Alliance to assess why they lost. Mermista quickly takes over, jumping at the chance to play-act as an investigator like in her favorite "Mer-Mystery" novels. Unwittingly, she is actually correct about a spy being in their midst. However, her insistence in interrogating nearly everyone in Bright Moon, including people who were not present at the battle of Dryl, and interrogating people about "murder" that did not happen, results in nothing but confusion.
Meanwhile, Flutterina reports back to Catra on the developments, utterly unconcerned about Mermista's attempts to discover her. As Mermista's "investigation" continues, they uncover contradictory testimonials from officers and Princesses about receiving orders from different Princesses when they were ostensibly somewhere else, who had no recollection of giving such orders, but Mermista promptly discards this. At the same time, Bow becomes convinced that he is actually the spy, to everyone's consternation.
While the investigation lumbers on, Adora interrogates Shadow Weaver, convinced that she is the spy. Shadow Weaver claims to have just been making tea in her garden even as Adora rounds on Glimmer for letting Shadow Weaver walk around without her guards. When the argument escalates, Shadow Weaver steps in to calm things, but Adora remains suspicious.
Adora and Glimmer interrogate Flutterina next, who quickly gets them to arguing about Shadow Weaver again. They then continue to investigate Sea Hawk, who cannot restrain himself from exaggerating his exploits in battle, and then several kitchen staff who weren't even present at the battle, followed by Bow who once again insisted that his "evil alter-ego" is responsible for the crime.
Frustrated, Glimmer planned to head out alone to strike at the Horde, but Adora convinced her to stay until they get news of the War Room communications panel being sabotaged. Again, the Princesses have conflicting stories about who was in the room, with Mermista claiming not to have been there despite Frosta supposedly having seen her leave the room.
At their wits end, Adora and Glimmer finally drop all excuses of an investigation and take counsel from Shadow Weaver. She comes up with a plan to talk about a "backup" communication device so that the person who destroyed the original would go after it, followed by the Princesses pretending to argue seriously enough that the traitor would take the opportunity to slip away. Adora and Glimmer then execute the plan, and the moment after Flutterina leaves, they stop arguing and follow, cornering Flutterina in the dining room. Flutterina attempts to flee, but Shadow Weaver had helped Glimmer to place a trap spell at the entrance, imprisoning Flutterina.
Rather than staying silent until an opportunity presented itself to escape and transform into another trusted person to slip away, instead Flutterina immediately revealed her sources and methods. She revealed her shape-shifting abilities, how she transformed into different Princesses during the battle of Dryl in order to give sabotaging orders, and also revealed that Flutterina was actually Double Trouble in disguise, working for Catra.
Finally, Double Trouble revealed yet more sensitive information about the Horde. Instead of leaving the Princesses ignorant and inactive until word reached them, Double Trouble willingly told them early about how the Battle of Salineas had already taken place, that Salineas had fallen to Hordak, and that the Horde was surging through the gate and taking the seas even now. Double Trouble outright gloated about how the entire exercise was merely to stall the Princesses until the battle was over, revealing yet more methods.
Distraught over the loss of Salineas, Glimmer quickly teleported directly there, where Mermista broke down at the sight of her fallen and ruined city. Enraged, Glimmer vowed to retake Salineas and all of Etheria, even as Hordak and Catra celebrated their victory. Out in space, meanwhile, Horde Prime is seen leading his armada inside his massive ship, then suddenly grins sinisterly.
- Adora/She-Ra (Aimee Carrero)
- Baker, Soda Pop, and Busgirl (Grey Griffin/Jordan Fisher/Dana Davis)
- Bow (Marcus Scribner)
- Bright Moon General
- Catra (AJ Michalka)
- Double Trouble/Flutterina (Jacob Tobia/Amanda Celine Miller)
- Frosta (Merit Leighton)
- Glimmer (Karen Fukuhara)
- This episode takes influence from noir detective films, as evidenced by the jazz music and monochrome color scheme in some scenes, as well as the mystery plot.