When Elyse's sister Michele and her family arrives for their annual visit, Elyse is overjoyed, while the rest of the Keaton clan brace themselves for a long hard week of togetherness.

With the exception of Elyse, who loves spending time with her sister, each of the Keatons is hard pressed to be gracious about the situation. Steven is constantly being needled by Michele's husband Marv; Michele's daughter Monica becomes the resident prophet of doom and gloom; and Monica's brother Marv Jr. begins appropriating Alex's clothes.

Oblivious to the Keatons' hospitality, insomniac Marv serenades the household with bagpipe tunes late at night, accepts collect calls from his business associates on the Keatons' phone, and generally drives everyone crazy. It is only after he demolishes the back end of the Keatons' car, however, that the usually tolerant Steven jumps up to defend hearth and home.