Invader on My Back — Philip E. High

In the far future, the world has fallen to chaos with the criminal elements controlling the cities and vast police forces ruling the unknown wilderness beyond.

Only one man, unknowingly, holds the key to the state in which society finds itself - a man named Craig.

Craig, however, is an outcast, a pariah, feared by organised crime and despised by the police who, despite themselves, are compelled to use him.

This is the tale of how Craig fights back - against forces unknown - and of his attempts to reinstate himself into a society that has rejected him.