The problem is the secret attack plan Voltron used to dispose of the comet before was lost when Voltron was split up so the VF has to hurry to try to rediscover this secret. Coran is certain they're doomed as it took Voltron 10 years to find the secret before but the Princess is stubbornly optimistic along with the rest of the team and they launch the Lions. Wasting no time, they approach the comet and try blasting it off course, which doesn't work (like it would take 10 years to figure that out lol Not gonna be that simple, guys!). In a fantastic turn of treachery, Lotor and Haggar 'let it slip' about the secret attack plan in front of Romelle. Desperate to help, she gets on the radio and relays this misinformation to the team - unwittingly sealing their doom.
Voltron gets trapped on the comet's surface while Arus begins to feel the destructive effects of the comet's gravitational pull. Coran contacts the Alliance but they're reluctant to send help - the only available fleet is guarding their main power supply. Meanwhile, Haggar sends out a device called a metal ripper that begins chewing Voltron to bits. Bandor's (Princess Romelle's brother) fleet shows up just in time to save Voltron from the ripper. Unfortunately, the only way to save Arus is to sacrifice Voltron - Keith orders Bandor to fire at the comic with everything his star fleet's got. It succeeds in blasting the comet off course, but the fate of the Voltron force, still trapped on its surface, is unsure.
As the episode ends, Lotor is happy that the VF seem finished and indeed it looks like they died - though the voice over assures us they're in a deep sleep. But that might be more American censors at work. Anyway, this and the second part coming up are my second favorite eps after "The Sleeping Princess". Good stuff!