SPOILERS FOR THE EPISODE AND BASICALLY THE WHOLE SERIES…just as a heads up.
Summary: Steven helps a friend who’s afraid of thunderstorms.
They are really trying to be as vague as possible not to spoil the developments that have been happening these recent episodes. For those who missed the last episode, you’re no doubt surprised to see that Peridot is currently taking up residency in Steven’s bathroom. Basically she was defeated last time and had no choice but to stay in their as it seems to be the only place in Steven’s house with a locking door. This episode picks up moments later, Peridot still in the bathroom and the Crystal Gems deciding to leave for…Reasons? Anyways, they head out and leave Steven home alone with Peridot, who quickly becomes freaked out by thunder. Steven is quick to point out there is nothing to worry about and the two bond a little and Peridot agrees to tell him about The Cluster.
Heading to Kindergarten, the secret of The Cluster is revealed. A big secret about Earth and why there is so many Gem mutants everywhere is also revealed. It turns out way back when the Gems first decided to colonize Earth, they realized the planet wasn’t suitable to be a new home planet and instead decided to run experiments on it instead. All the monsters the cast has been fighting all this time have been experiments the Gem home world wanted to run just because they could. And The Cluster? Turns out it’s a giant mutant gem shard monster near the Earth’s core and when it wakes up the entire planet is going to be destroyed. Nifty huh?
Then a horde of Gem monsters show up and Steven and Peridot get cornered. Luckily they are saved by the Crystal Gems and Peridot realizes she has no choice but to cooperate. End of episode.
The big reveal about The Cluster, the secret of Earth, and Peridot finally realizing she needs to open up and trust the Crystal Gems are the real highlights of this episode. No longer in the bathroom and deciding to help make sure the Earth won’t blow up in the future, the next few episodes will no doubt show Peridot exploring the planet more and interacting with the Crystal Gems. Sounds like something to look forward to.