Jan's uptight husband Philip often clashes with Marcia's slovenly husband Wally. Philip is a college science professor and is several years older than Jan, while Wally is, when steadily working, a fun-loving salesman for a large toy company. Wally could be quite a slob compared to the Phillip, who was rather the neat freak.
Philip becomes so wrapped up in his work that he ignores the needs of Jan, and they separate as the two contemplate divorce. When they arrive at the Brady home for the Christmas family gathering, tensions continue between the troubled couple as Carol tries desperately to get the two, who were unwilling to even sleep together, to patch things up in their relationship. Somehow, the "Christmas Spirit" seems to take over them the whole Brady family after Mike, who had to rush to a construction site of a property which he initially had laid the architectural plans for before it fell into the hands of the businessman he designed it for, a quite unscrupulous sort, had cut corners on it, to rescue to workers trapped in the building. After Mike, who manages to rescue the construction workers, gets trapped himself in the building he, the entire family, the press and spectators appear at the site as the police are able to rescue Mike. The family then begins a rendition of "O Come All Ye Faithful", which seems to lead Wally and Jan, whose hearts are warmed by the rescue of Mike and the construction workers, to consider their circumstance, and to reconcile.
He and Jan, who is barren and cannot have children of her own, decide to adopt a Korean girl.