It's the ultimate in mass transit systems, a network of interstitial tunnels that bind the planets of the solar system together. Earth to Pluto in forty minutes with a supersave non-premium off-peak travelcard. But something is living in the network, chewing its way to the very heart of the system and leaving a trail of death and mutation behind it. Once again a reluctant Doctor is dragged into human history. Back down amongst the joyboys, freesurfers, chessfans, politicians, and floozies, where friends are more dangerous than enemies and one man's human being is another psychotic killing machine. Once again the Doctor is all that stands between humanity and its own mistakes.