Brander, security chief of the Syrtis Base on Mars, has been forced to invoke Emergency Directive SB-17-5Z. Two men have died, victims of an unknown alien disease. The entire base is now isolated. No one can enter or leave under any circumstances. Dr. John Naysmith, newly arrived on Mars, is leading a small medical team in a desperate attempt to isolate the virus and discover a serum to combat it. But if the disease continues to spread and gets out of control, then Brander will have no alternative but to annihilate the base and everyone in it with nuclear bombs! Only Naysmith can save the day-but will he be too late in solving?