From two hundred light years across the universe comes a message of terror. Ten years from now, a new radio telescope picks up from the constellation of Andromeda a complex series of signals which prove to be a programme for a giant computer. When the computer begins to relay the information it receives from Andromeda the project assumes a vital importance, scientists find themselves possessing knowledge previously unknown to mankind, knowledge that could threaten the security of human life itself. Sir Fred Hoyle was Plumian Professor of Astronomy and Experimental Philosophy at Cambridge University while John Elliott was a novelist, from their collaboration comes a work of major scientific interest and a remarkably original story that is as enthralling today.