The Baker Family begins to undergo many changes,beginning with Lorraine(Hillary Duff), and her desire to go study in New York. Their oldest daughter,Nora(Piper Perabo),is now married To Bud McNulty,and pregnant.
But the couple intend to move to Houston Texas,Because of Bud's new job promotion.
Feeling that the family is breaking apart,as the children grow up and move away.
Tom persuades the entire family to take one last family vacation all together At Lake Winnetka.
Tom's old rival Jimmy Murtaugh(Eugene Levy), and his large family are also there for the summer.
Jimmy constantly flaunts his wealth and success to Tom, as well of the accomplishemnts of his children,constantly suggesting to Tom that the Baker children are less successful,because of Tom's parenting style. During the movie, Sarah Baker and Elliot Murtaugh,go on a date,where they are spied on by their fathers. In the end of the movie, the Bakers and the Murtaughs,become friends, when during a canoe race, Nora goes into labor, and the 2 families,work together to get Nora to the hospital.
Nora gives birth to a baby boy,whom they name Tom.In the end,back at the lake Nora and Bud say good-bye to Nora's family,and Nora,Bud and the baby head off To Houston,Texas.