A space station orbiting Earth has lain dormant for 8,476 years. Its systems are clogged with dust, so the human crew kept frozen in cryogenic storage have never woken up. When the Doctor, Sarah and Harry arrive to resuscitate the sleepers, they discover something else on board. A small, golf-ball like object gives Harry an electric shock, and has a more sinister impact on the awakening crew. Soon, the Doctor and his friends are battling to save the space station - and Earth - from a ravenous puffball!