Zarkon has Lotor arrested for losing battle after battle against Voltron, and attempts to lead a fight himself. But the Voltron Force succeeds in beating him back before he can topple the Polstar Canon. They actually intend to use this canon to boost them out of Arus' orbit to Doom. In this way they can destroy Zarkon's arsenal there to free the enslaved. But Zarkon and Lotor both get a surprise when the Drule Empire hears of the defeat. They're willing to bet that Lotor could do better than Zarkon, and tell him to arrest Zarkon in the same manner when he returns home. Lotor decides it will be a win-win situation if he forces Zarkon to pilot a giant robot to do battle when Voltron arrives...
—brainybrailler@comcast.net