Things could be better for Max (CAYDEN BOYD), an imaginative fourth grader. Not only are his parents (DAVID ARQUETTE AND KRISTIN DAVIS) always fighting and his teacher, Mr. Electricidad (GEORGE LOPEZ), complaining that he spends too much of his time dreaming, but the class bully Linus (JACOB DAVICH) has just stolen and defiled his dream journal.
That's where he keeps notes about various characters such as Sharkboy -- a kid raised by sharks -- and Lavagirl -- who can control her namesake material and wield it as a weapon -- who he believes are real but only get him grief from Linus and the other kids. Everyone else, however, becomes believers when a tornado strikes the school and Sharkboy (TAYLOR LAUTNER) and Lavagirl (TAYLOR DOOLEY) suddenly show up, stating they need Max to return with them to Planet Drool.
It seems that villain Mr. Electric (GEORGE LOPEZ) and his sidekick Minus (JACOB DAVICH) have set out to gain control of the cerebral planet by destroying all dreams, including Sharkboy and Lavagirl. From that point on, Max rediscovers his forgotten and discarded dreams as he joins forces with his two new friends in battling Mr. Electric and his minions to save Planet Drool.