Sam Neill transports us into the murky and terrifying world of the universe's ultimate monster - the black hole. They are only ten miles across, but they can rip apart a star of a million miles or more. Black holes are gravity gone mad. There should be ten million of them in our galaxy - but we have only found two hundred of them. So are black holes any threat to us here on Earth? Sam's voyage of discovery ends with a look at what would happen if our planet even encountered one of these interstellar destroyers.