A rescue mission to Mars finds only one survivor of the first expedition, who claims that the rest of them were killed by something unknown. On the way back to Earth, they discover that "it" has stowed away on their ship, and may kill them all before they can get back home. Marshall Thompson as Col. Edward Carruthers Shawn Smith as Ann Anderson Kim Spalding as Col. Van Heusen Ann Doran as Mary Royce Dabbs Greer as Eric Royce Paul Langton as Lt. James Calder Robert Bice as Maj. John Purdue