Season synopsis
Contains spoilers for this season and earlier seasons.
Bubblegum and Marceline enter Ice King’s malfunctioning crown, where a digital Betty is interfering with its circuitry. Inside, Marceline encounters Simon, who persuades the program to stop. Later, Finn’s Grass Sword damages the Finn Sword, and their eventual merging creates Fern, a grass-bodied double of Finn. Finn loses his regrown arm and receives a mechanical replacement. The search for other humans then takes Finn, Jake, BMO and Susan Strong across the ocean, through islands that include a community retreating into virtual reality.
Susan gradually remembers that she was Kara, a seeker trained to retrieve people who tried to leave the human islands. She had stopped her friend Frieda from escaping under Dr. Gross’s control. On Founders’ Island, Finn meets his mother, Minerva Campbell, and learns that she uploaded her consciousness into a digital network after a deadly virus struck the human community. Minerva built robotic helpers to protect people and wants Finn to remain with her. Finn shares what he has learned about life in Ooo; Minerva relents, and abandons her plan to upload the islanders’ minds against their will. Kara and Frieda reconcile and set off on their own journey. Finn says goodbye to Minerva through a virtual-reality headset before returning to Ooo with Jake and BMO.