Storm Over Warlock by Andre Norton

The mist was not a quiet thing; it billowed and curled until it appeared to half-conceal darker shadows, any one of which could be an enemy. Shann remained hunkered on the sand, every sense abnormally alert, watching the fog. He was still sure he could hear sounds which marked the progress of another. What other? One of the Warlockians tracking him to spy? Or was there some prisoner like himself lost out there in the murk? Could it be Thorvald?

Now the sound had ceased. He was not even sure from what direction it had first come. Perhaps that other was listening now, as intent upon locating him. Shann ran his tongue over dry lips. The impulse to call out, to try and contact any fellow traveler here, was strong. Only hard-learned caution kept him silent. He got to his hands and knees, uncertain as to his previous direction.