Beavis and Butt-head are two juveniles whose life is watching MTV. When their TV is stolen, the two set out to find a replacement set. Neither are quick on the uptake and thus inadvertently get involved in a murder-for-hire case involving a man, Muddy, who wants to bump off his wife, Dallas. The boys, however, think they've been hired to have sex with the woman. When they finally encounter her, she hides a top-secret biological weapon, the X-5 virus unit, in Beavis' pants and sends them to Washington where she says she'll later meet them. Little do they know that the government is after them and the device and Agent Fleming will do anything to get it back. As they board a tour bus headed for D.C., they get to meet many people, including an elderly lady on a bus and tour the country.