A retired army lieutenant recruits his children to help him finish building his Doomsday Castle, a completely self-sufficient fortress of refuge for the End of Days. The most important tasks are building a drawbridge for the front door, cleaning out the bunker, where the family will be living and fortifying the remaining weaknesses inside of the bunker. The children must work together to complete their father's vision, and be prepared for the Apocalypse.

Some of the family is tested on obtaining their own sources of food for the castle while Brent Sr. and Dawn Marie build a catapult to be able to defend the castle from intruders when the end times come. Lindsey and Ashley find a sustainable food source while Brent II and Michael hunt for a meal. The entire family tests the catapult together and then feasts on their new food options.

A military expert is brought in to train the family on how to defend the Castle as it stands now. The family comes together to build a solar powered water system. However, tensions flare when communication is broken down and the family can't work together. Their military training is tested and things come to a head when a mock ambush pushes the family to their limits.