Imagine the universe as a forest, patrolled by numberless and nameless predators. In this forest, stealth is survival - any civilisation that reveals its location is prey. Earth has. Now the predators are coming. Crossing light years, they will reach Earth in four centuries' time. But the sophons, their extra-dimensional agents and saboteurs, are already here. Only the individual human mind remains immune to their influence. This is the motivation for the Wallfacer Project, a last-ditch defence