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 torrential downpour gives the kids time to have some fun in the mud. What starts out as fun and games turns into the breaking point for Ashley as Lindsey and Dawn-Marie gang up on her. Tensions run high and the family splits apart as fights develop. Ashley, Michael and Brent II work on a listening/observation post in the woods while Brent Sr. and Dawn-Marie continue work on a portcullis..

Brent Sr. launches a fake tear gas attack on the children to test their readiness, as well as to stress the importance of having barriers on the castle windows. Have they improved since the first ambush test? Brent Sr. sends Brent II and Ashley out to source materials to shutter the windows, while Michael and Dawn-Marie are put in charge of planting a survival garden.

Ashley is sleeping out in the family's fort in the woods when she senses an intruder and sounds the foghorn. Brent Sr. and Michael get her safely out, but for the first time, the family is facing a threat from an unknown entity Â-- something they expect much more of in the future. Brent Sr. tasks Michael and Dawn-Marie with developing a multi-level perimeter defense system to deter enemies from getting too close to the castle.

Brent Sr. teaches his kids how to rappel off the roof of the castle in case the castle is attacked and they need to quickly escape. Brent II quickly realizes that their enemies could still be on the ground waiting for them and comes up with a solution: a zip line. Brent II and Michael scout out the best path for the zip line, and Lindsey is instructed to help her dad with the roof.

Brent Sr. is plotting to test the skills his children have developed in the past few months, from honing defensive techniques to building sustainable food sources and devising combat operations. He's enlisting his friend Military Mike to do a comprehensive walk-through of their work on the castle grounds to determine whether this massive fortress will protect them in a doomsday scenario. Brent Sr. strategizes a mock siege and surgical strike that will put his children to the ultimate test.