Spaceship to the Unknown is a condensed version of the original serial, compressing the original twelve episodes into an efficient 97 minute feature. Flash Gordon (Buster Crabbe) heads into space with brilliant scientist Dr. Zarkoff (Frank Shannon) and his sweetheart Dale Arden (Jean Rogers) in an effort to throw the planet Mongo off course; it is expected to crash into the Earth within a matter of days. However, once Flash and his crew arrive on Mongo, they have to deal with the supremely evil Ming the Merciless (Charles B. Middleton) and his wicked minions.