Telempath by Spider Robinson - 1986

Spider's 1976 first novel, in its umpteenth reincarnation.

Isham Stone is the second-best assassin left in a shattered world. He's many miles from home, half-dead, his left arm is gangrenous, and he possesses--like everyone else--a sense of smell 1000 times better than a wolf's. Ahead of him, in the stinking ruins of New York, hides Carlson, the greatest killer of all time. All Isham has to do is stay alive long enough to find Carlson and kill him. But Carlson is guarded by ghosts. They rode the winds when Earth was bubbling rock, shared the world with men for a million years, and though we sensed their presence we never truly believed in them--for in our arrogance we assumed life was an exclusive property of solids and liquids... Now they've declared war on us, and our species is nearly annihilated...thanks to the man Isham has come to kill.

The first third of this book, as "By Any Other Name," won the Hugo Award for Best Novella, the first of Spider's 3 Hugos.