The crew of the Tantalus Base is ready to finish the activities in Mars and preparing to return to Earth after a six months mission on the Red Planet. One member of crew discovers fossilized evidence of bacterial life. Unwilling to let the relief crew claims all the glory, he disobeys orders to pack up and goes out on an unauthorized expedition to collect further samples. But a routine excavation turns to disaster when the porous ground collapses and he falls into a deep crevice and near certain death. His devastated colleagues attempt to recover his body. However, when another vanishes, they start to suspect that the life-form they have discovered is not without danger..