Possession is the twenty-first episode of the Beast Wars TV series.
A violent storm rages, causing significant damage and knocking out power to both the Maximal and Predacon bases. While the Maximals stash their extra ammo deeper in their ship's hold to prevent undue accidents, Waspinator attempts to get one of the Predacon base's computer consoles online...only to be greeted by a ghostly, shrill voice from it. A power surge hits the bug-bot soon afterwards, and when the other Predacons begin to wonder what has happened to him, in he comes, announcing his return "at long last" in the same eerie voice.
The voice belongs to Starscream, Air Commander of the Decepticon forces and second-in-command to the original Megatron, whose spark had been tumbling through time and space for an unknown number of years before settling within Waspinator. As he puts it, he was destroyed defending Galvatron from the Chaos Bringer Unicron, but his spark endured. As a show of his good faith, he pledges his loyalty to the Predacon Megatron, revealing vital information about the state of the Maximal base due to the storm, intelligence Megatron could use to plan a sneak attack. Intrigued by the idea, Megatron accepts Starscream into his ranks.
The next day, as the Maximals are making repairs to their base, they are suddenly attacked by the Preds, and Starscream's intel proves very useful in catching them off-guard. In the ensuing firefight, Dinobot is injured and the Decepticon Air Commander flies rings round Optimus Primal, forcing the Maximals to abandon ship and regroup outside. Happy with their victory, Megatron puts Starscream in charge of holding the Axalon, with Scorponok and Blackarachnia under his command, while the rest of the Predacons return to their base, in case the Maximals decide to go for a sneak attack of their own. However, despite being pleased with Starscream's help, Megatron warns Scorponok in private to watch their new ally closely. Once they're alone, though, Blackarachnia shows off her knack for history by correctly pointing out to Starscream that he was murdered by Galvatron after he betrayed the Decepticon commander. She's willing to keep this a secret, though, if she's let in on his real plans: to destabilize Megatron's control and rule both factions.
Realizing Starscream's tendencies, Optimus Primal leads the Maximals in returning to the Axalon and calling Starscream out to announce their surrender, citing the need to use the ship's CR chamber to repair Dinobot's (now exaggerated) wounds. Feeling generous, the Decepticon Air Commander allows Optimus and Dinobot to come on board, but as predictably as night follows day, betrays them and strips Optimus of his weapons and locks him up in the hold as soon as he steps on deck. With their leader now his prisoner, Starscream orders the other Maximals to attack the Predacon base, over the token objections of Scorponok, who is then blasted away by Starscream and Blackarachnia. They comply, and the trap is set.
Unbeknown to the Air Commander, he's been duped by the oldest trick in the book; by allowing himself to be betrayed, Optimus Primal has put himself and Dinobot in the perfect position to retake their base, which they do in a dazzling display that forces Starscream and Blackarachnia to retreat back to Predacon territory. Upon hearing of the Maximal attack that is ordered by Starscream, Megatron angrily swears to finish both Starscream and Blackarachnia off to himself. Optimus pursues and manages to best the Decepticon in an aerial dogfight, leaving him grovelling at the Maximal's feet...until Blackarachnia shows up, prompting Starscream to plead for her aid, believing they can still complete their coup. No dice; this new generation is much less gullible than their ancestors, and Blackarachnia has skillfully pulled off a double-cross on the double-crosser, igniting a small energon cache underneath Starscream to "exorcise" the Decepticon's spark from Waspinator's body.
At the end of the day, Megatron gets done fixing the back-to-normal Waspinator as Blackarachnia explains her betrayal; if she hadn't done it, she maintains, she wouldn't have been able to sniff out Starscream's true motives. Megatron reluctantly accepts this excuse, but warns her that it still doesn't invoke confidence in her loyalties. Back at the Axalon, the Maximals are finishing up repairs of their own...everyone but Cheetor, who's slacking off with a bout of stargazing, quipping "Twinkle, twinkle, little Starscream," as the camera pans up to beyond the planet's orbit, showing Starscream's spark screaming mech fluid-drenched vengeance on all within the Beast Wars as he drifts away into the void.