Candace and the boys visit their grandparents at a lake house and the boys try to scare her with a fake Bigfoot while Doofenshmirtz goes out on a date and Perry gets ends up in the middle of it.

Candace plans a special birthday for Mom, and even a song, but Phineas and Ferb are always getting in her way of what she planned, unintentionally topping everything. Meanwhile, Doofenshmirtz creates a shrinking machine that will make whatever he hates implode.