In a bid to destroy the Galaxy Alliance, evil King Zarkon joins forces with the leader of the Drule Empire, Viceroy Throk. They create the largest armada of destroyers that has ever been seen in space. When this Fleet of Doom begins obliterating one key Galaxy Alliance outpost after another, they realize the threat is too great even for one of the mighty Voltron units to deal with. Therefore, they send the call both to the stellar ship Explorer and to the Castle of Lions. Keith, Princess Allura, Hunk, Lance and Pidge fly into battle in their robot lions, alongside Commanders Jeff, Krik and Cliff with their vehicle teams. When Prince Lotor arrives as the head of a super Robeast made of five united Robeasts, Keith and Jeff give the order to form both Voltrons! Haggar targets Keith and Allura with a curse, and the Fleet of Doom is closing in on Galaxy Garrison. The ultimate giant robot team-up is Earth's last hope!