Valley of Thracians by Ellis Shuman
A Peace Corps volunteer has gone missing in Bulgaria and everyone assumes he is dead, everyone except his grandfather, who refuses to give up hope. Retired literature professor Simon Matthews launches a desperate search only to be lured into a bizarre quest to retrieve a stolen Thracian artifact—a unique object of immense value others will stop at nothing to recover.
Matthews travels through a Balkan landscape dotted with ancient tombs and fortresses, unaware that his grandson has been confined to an isolated mountain cabin, slowly recovering from a severe head injury. Nothing can be taken at face value, as the woman assisting Matthews in his quest and the nurse caring for his injured grandson may have ulterior motives in helping the two reunite. Even when Matthews succeeds in joining up with his grandson, departure from Bulgaria is only possible if the missing relic can be found.