School is out for summer and step brothers Phineas and Ferb decide to make each day an adventure from building a death defying rollercoaster or 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.