Drake and Josh are desperate to ride the awesome new roller-coaster, the Demonator, at their favorite amusement park, Mystic Mountain. However, their parents, who are going out for the night, force the boys to stay home and watch over their great-grandfather, who's recovering from surgery. After their parents leave, Drake issues the help of their geeky friends, Craig and Eric, to watch over the grandfather, while Drake, Josh, and Megan (who they agree to take after she threatens to tattle on them) jet off to ride the Demonator. However, nothing goes according to plan; due to Josh's emergency bathroom break and wrestling the park's mascot, they get sent to the back of the line more than once. Meanwhile, back at the house, the grandfather, who believes he is fighting in World War 2 due to pain medication, tries to hold Craig and Eric hostage.