The boys build a rollercoaster while their mother is out shopping; have an unusual birthday surprise for Candace; and enter a car race.
The boys meet the Lake Nose Monster; build a device that allows animals to air their grievances; and offer their father a clue to complete a crossword.
The boys build a biodome in their back yard; invent super-fast boots for Candace; and race their hot-air balloons to the top of a mountain.
The boys plan their own New Year's Eve ball drop; create a new invention using recycled parts from past projects; and make a giant inflatable wading pool.
School's out for the summer, and stepbrothers Phineas and Ferb decide to make each day an adventure, from building a death-defying rollercoaster to surfing tidal waves to locating Frankenstein's brain. Their bold escapades always end up cramping the style of their teenaged sister, Candace, who makes every attempt to expose Mom to what is really going on, but somehow always seems to fail. Meanwhile, the family's simple-minded pet platypus leads a double life as secret Agent P and faces off with the evil Dr. Doofenshmirtz to save the world. There's a whole lot of stuff to do before school starts and Phineas and Ferb plan to do it all.