The Midwest USA is invaded by stingray-shaped alien slugs that ride on people's backs and control their minds in order to spread their dominion. Government agency reps Sam Givens, Andrew Nivens, and Mary Sefton must stop the aliens.
| Actor | Role |
|---|---|
 Donald SutherlandAndrew Nivens | Andrew Nivens |
 Eric ThalSam Nivens | Sam Nivens |
 Julie WarnerMary Sefton | Mary Sefton |
 Keith DavidAlex Holland | Alex Holland |
 Will PattonDr. Lawrence Graves | Dr. Lawrence Graves |
 Richard BelzerNeil Jarvis | Neil Jarvis |
 Tom MasonPresident Douglas | President Douglas |
 Yaphet KottoRessler | Ressler |
 Gerry BammanViscott | Viscott |
 Sam AndersonCulbertson | Culbertson |
 J. Patrick McCormackGidding | Gidding |
 Marshall BellGeneral Morgan | General Morgan |
| NNicholas CasconeGreenberg | Greenberg |
 Bruce JarchowBarnes | Barnes |
 Benjamin MoutonHiggins | Higgins |
 Donna GarrettMiss Haines | Miss Haines |
 Andrew RobinsonHawthorne | Hawthorne |
 Bill BlairSlugged Businessman (uncredited) | Slugged Businessman (uncredited) |
| EEric Briant WellsVince Hayward | Vince Hayward |
 David PasquesiNot listed | Not listed |