Doctor Who: Diamond Dogs

"Here on Saturn, it literally rains diamonds."
For over fifteen years the crew of Kollo-Zarnista Mining Facility 27 has been extracting diamonds from deep within the atmosphere of Saturn, diamonds that help to fund the ever-expanding Human Empire. But when a mining operation goes wrong, a rescue mission must be launched to save a worker lost overboard, a worker who claims that he has seen something amongst the swirling clouds. Something that can't possibly exist.