Previously on Steven Universe…
A hundred years earlier, Obsidian had been possessed by the evil Sludge that was covering Planet Zorak. While the other Gems had presumed him dead, Ruby believed that he was still alive. Her belief was confirmed when Obsidian appeared near the Warp Pad on Planet Zorak. She was elated at his return, but was horrified when he rejected her. Obsidian told the other Gems that he was going to rule the universe and disappeared as mysteriously as he had reappeared. Ruby still wasn't shaken. After the real Obsidian spoke to her in a dream, she knew he needed help. She warped to Beach City without telling the other Gems, and was ambushed by Obsidian. The other Gems came to her rescue, but Obsidian had gone completely insane. Ruby knew there was only one thing to do. She ran him through with her spear, and Garnet cleansed his Gems of the Sludge.
Meanwhile, Peridot professed her love for Pearl through a kiss in battle. In the end, Pearl & Peridot ended up together and Ruby & Obsidian resumed dating. But the threat of the Sludge is still high. The Sludge has taken over three-fourths of Planet Zorak. Obsidian has sworn to destroy the Sludge at all costs…