The Chasm — Victor Canning

A novel set in Florence in 1946. The city is in ruins and shell-shocked officer Edward Burgess keeps seeing old comrades as he wanders the streets. But no, the comrades are dead and all he sees are ghosts. Except in one case, and that one man would much rather people believed he was dead. The scene moves to a remote Apennine village, a love blossoming and then a lethal confrontation.