Earthfall - Mark Walden

Sam wakes to see strange vessels gathered in the skies around London. As he stares up, people stream past, walking silently towards the enormous ships which emit a persistent noise. Only Sam seems immune to the signal.

Six months later, Sam is absolutely alone. Injured by one of the flying drones which now populate London, Sam realises that without medical supplies he will die. Venturing above ground he is attacked again, but this time the drone is shot down in a hail of machine gun fire. In five minutes Sam learns two things: he is not alone; the drone injury should have killed him instantly - yet he is still alive. The battle for Earth is about to begin.