At the start of the film, the US Government has ordered a branch of the US Military to discontinue tests concerning "the C.H.U.D. project", which is built around the idea that enzymes taken from the sewer dwelling creatures from C.H.U.D. can make hyper-effective killing machines in the army. For reasons that are unclear even to those who watch the film, the last specimen of the experiment (BUD the C.H.U.D.) is hidden away in a Centre for Disease Control in a small American town, where a trio of bumbling teenagers accidentally steal and reawaken him. Bud escapes and begins to forge an army of C.H.U.D.s.