Zarkon is annoyed at all the happiness on Arus, so in the dead of night, he sends out a Robeast to start destroying Arusian cities. The Castle's alert sirens go off and it isn't long before the VF launch into action. This crab-like Robeast is a real challenge. What's worse is they're hesitant to use Voltron as the monster insists on staying in the city where frightened Arusians could be hurt by the resulting battle. The VF try to lure the Robeast away but he won't budge, and Pidge only succeeds in getting his Lion skewered by the Robeast.