Thirty years before, back in the 1980s, a rocket ship was launched to Ursa Major, a destination so distant that the crew were frozen for the journey to prevent ageing while they were away. But the DSP 15 did not return, and one by one space stations throughout the world ceased to transmit the signal that would bring it home.
Then, unexpectedly, it was spotted on the radar at Mildenhall. It landed safely, but with it came a terrifying message: “If this ship returns to Earth, then mankind is in deadly peril – God help you –”
Novelisation of the BBC TV series