After an introduction from the Diamonds and the story of Steven, Steven Universe (now 16 years old) greets the citizens of the Gem Homeworld and other colonies through a broadcast, announcing that he's done dismantling the empire and is going back to live with his friends on Earth. The Diamonds want him to stay to fulfill Pink Diamond's role as a leader, but he refuses. Back on Earth, Connie welcomes Steven back and he sees her off to space camp. Steven, Pearl, Garnet, and Amethyst celebrate their newfound "Happily ever after".
Almost immediately afterward, a giant drill lands on the hillside of Beach City and Spinel, a deranged, cartoonish Gem, appears, announcing her intent to kill Steven and the rest of the life on Earth. Using a scythe-like weapon, she poofs Pearl, Garnet, and Amethyst. Her attacks also weaken Steven's Gem powers, though his body is unharmed. Steven manages to steal her scythe and poof Spinel.
Back at the beach house, Steven calls his father, Greg, for help. The Gems regenerate their bodies (including Ruby and Sapphire separately), but their memories have been erased; with Pearl assuming that she is Greg's servant. With her memories gone, Spinel is a goofy and happy-go-lucky Gem whose role is to entertain her companion (Steven). Steven and Spinel take Ruby and Sapphire to seek advice from Peridot, Lapis Lazuli and Bismuth.
SU Movie 770Bismuth identifies Spinel's scythe as a "Rejuvenator", a device that can reset the mind of a Gem back to when it was first created. While Steven didn't reset thanks to his human half but is discouraged from the loss of his powers from his gem half taking the hit. The three of them encourage Steven not to give up. Spinel compares the situation to a puzzle, suggesting that they find the Gems' "missing pieces" to restore their memories, inspiring Steven to try to reenact Ruby and Sapphire's first fusion. Spinel's antics cause scaffolding to collapse, almost crushing Ruby; when Sapphire shoves her to safety, the pair fuse into Garnet, but she still has no memory of her life.SU
After Steven recovers Amethyst's memory by reenacting experiences the two had together, Peridot discovers that the drill is injecting a toxic chemical that will kill all life on Earth. They then come to the conclusion that Spinel would be the one to remove the Injector, so they need to bring her memories back. Steven remembers back when Spinel attacked them, Pearl seemed to know who she was. In order to revive Pearl's memory, the group takes her to a Sadie Killer and the Suspects concert, in the hope their music will bring back her memories of rebellion, but Pearl says that as long as Greg exists she will obey him. Steven uses what little energy he has left to fuse with Greg, which enables Pearl to recover her memory. She tells Steven that Spinel was once Pink Diamond's playmate; Spinel is suddenly overcome with sadness and flees.
After sending Lion for Connie, Steven finds Spinel crying at his house. She takes Steven to a desolate garden in space and reveals her backstory: she was Pink Diamond's playmate until the other Diamonds gave Pink her own colony. Pink told Spinel to wait for her and left her alone in the garden for 6,000 years until she learned of Pink Diamond's fate via Steven's broadcast from the beginning of the movie. Steven then tells her that she isn't the only one Pink hurt and that she should find a better friend who won't hurt her.
Steven Rediscovering His PowersBack in Beach City, Spinel turns off the drill, but when Steven begins shifting his attention back to everyone else, she accuses Steven of just using her and then abandoning her or planning to wipe her memory again after discovering that he kept the Rejuvenator with him (but in reality, had nowhere else to put it). She turns the drill back on and attacks Steven. As he tries to explain the truth to her, Garnet recovers her memory. Steven sends the others out to rescue the humans of Beach City while he confronts Spinel. Steven finally realizes why his Gem powers have not yet returned: his desire for an unchanging "happily ever after" has left him resistant to the very notion of growth and change, which he needs to re-experience. Embracing this fact, he regains his powers and battles Spinel. Their fight destroys the drill, and Spinel realizes that hurting Steven will not make her feel better, and relents.SU Movie 1998
The Diamonds suddenly arrive and state their intention to live on Earth with Steven. He introduces Spinel to them and they take an immediate liking to her and her goofy personality. The Diamonds accept her in place of Steven and she happily goes with them, now with people who will love her unconditionally. Steven and his friends gather to rebuild Beach City, thanks in part to Steven's healing powers undoing the damage of the poison. Steven, Pearl, Garnet, Amethyst, Connie, and Greg perform the Broadway-style song, "Finale".
