When a decaying Russian satellite crashes on the island, the Professor uses a key component for a barometer. With that device, he learns that a massive wave is going to swamp the island. In desperation, the castaways lash their huts together into one structure in order to have any chance to ride the disaster out.

Almost 20 years after the start of the original "Brady Bunch" the kids are grown up and have kids of their own. Everyone is having a wonderful time back at the family house for Christmas, until Mike learns of a structural problem in one of the buildings he designed. As he is inspecting the problem, the building collapses, trapping him inside. As the whole family waits by the pile of rubble, they fear the worst. Will Dad be all right?