Eddie wants Herman to come home because he promised him a new kite. On the way home, Herman passes a building where men are lifting a 300-pound safe. Herman walks under it, just as the rope breaks. The safe comes crashing down on Herman, and the men think it flattened his head. They tell him they'll get an ambulance, but he says he feels fine. Unfortunately, he can't remember his name.
That evening, the Munsters are worried about what happened to Herman. Grandpa turns on My Three Sons, which is interrupted to show breaking news of an amnesia person. "That's not John Doe," Eddie comments when he sees his father's picture. Lily and Grandpa go to claim Herman. The officers tell them not to tell Herman who he is because it might put him in shock. They hope he will just remember. They bring Herman out, and he has no recollection whatsoever of his wife and father-in-law.
Lily decides to adopt Herman, or John, as he is now known. Herman is excited to be adopted. The whole family acts as if Eddie and "John" are brothers. Lily buys Eddie his kite, to keep the promise made by Herman. "John" thinks Lily favors Eddie, but of course she doesn't. Several days pass by, but Herman still doesn't remember his identity.
Grandpa has an idea--he can pretend to be Lily's boyfriend, and see if jealousy will bring Herman out of it. He disguises himself, and acts very affectionately toward Lily. Herman, however, still acts as a child. Marilyn comes running downstairs, telling them that Eddie went on the roof. They all run outside, where Eddie is flying his kite on the roof. "Go inside! Go inside!" Lily yells. Herman is mortified. "Eddie, this is your father speaking!" Eddie falls off the roof, and Herman catches him. "That was a very stupid thing to do," he scolds. Herman tells Marilyn she can't be outside without a sweater, and tells Grandpa he should get out of his ridiculous outfit. Herman is unaware anything was wrong.
The next morning, Eddie says it was fun having Herman as his brother. Herman has been told, and explains that family love is thicker than amnesia. Everyone is glad Herman is back.