Pidge had brought a space mouse with him, and it's the little rodent that returns to tell the VF what happened. While Keith holds off some skeleton warriors outside the mystery castle, the others go inside - and get trapped too. Then they get their bell rung - literally.
A Robeast with grapples appears to haul the castle to Doom. Keith tries to follow by crawling up one of the grapples, but is knocked off. Luckily, he falls on one of the Doom fighter ships. After fighting his way inside and taking over, he flies it to his Lion. Using his lion's mouth-saber, he cuts the grapples sending the castle falling to earth. The force of the impact frees his friends and they're off to help finish off the Robeast.