The hunt for aliens is on! After a distinguished career in cosmology Professor Martin Rees, the Astronomer Royal, has taken up the search for extra-terrestrials. Looking for aliens is no longer science fiction - it's a question that's engaging some of the greatest minds in science. Many now think that we live in a galaxy with a billion Earth-like planets, some of which may be teeming with life. But what kind of life? Has anything evolved into beings we could communicate with? This documentary considers one of the most exciting and profound questions we can ask - are we alone in the universe?