Looking for a story I read in the 1970s about a pilot whose friend crashed in the jungle during the war.
He returns after the war to where he thinks the friend crashed and hires local natives to help search. The natives become uneasy and play drums at night to protect themselves from being taken by shadow people. The pilot is drawn away from the group and the drums and is then confronted by shadow people.
They explain that they found his dying friend and could only save him by converting him to a shadow. The pilot meets his friend again in shadow form, and is told that shadow people fight a battle every night against aliens that want to invade Earth.