Who are the parents of the person that emulates the man that is visiting?
One evening, a man claiming to be Carol's long-lost first husband, Roy Martin, shows up at the suburban Brady residence. The Bradys believe his story about suffering from amnesia and having plastic surgery after being injured. Mike has been planning a second wedding/renewal of vows for himself and Carol, for an anniversary present without her knowing, although Roy's arrival throws a monkey wrench into things. Throughout Roy's stay, he is openly hostile to them, his sarcasm and insults completely going over their heads. Peter, who is trying to decide what career path to choose, starts idolizing and emulating Roy, which frequently gets him in trouble at the architect firm where Mike works. 
Greg and Marcia both want to move out of their shared rooms and when neither wants to back down, they have to share the attic together. When Roy's arrival suggests that Carol and Mike might not be married, Greg and Marcia believe that they are technically not related. This leads them to realize they are in love with each other, but try to hide it from one another throughout the movie. Eventually both cave in and they share a kiss at the end of the movie, but Marcia agrees to let Greg have the attic to himself, until he goes to college.
Mike Carol