Clifford D. Simak 
Fellowship of the Talisman 

This was medieval England in the 1970s, again beset by the ancient Evil that had kept the Dark Ages from ever lightening. Half the country was in the grip of the fell Harriers, and it was through these Harried Lands that Duncan of Standish would have to make his way to Oxenford. His mission was to authenticate a long-lost testament which offered the only hope against the terror.Beset by Harriers, Duncan is saved by Diane, great-granddaughter of a renegade wizard, and joined by the strangest company ever assembled: a timid hermit, a ghost who knows nothing of ghosthood, a banshee, a grumpy goblin, a witch who could never quite make herself evil enough, and a demon who is AWOL from Hell.Duncan believes himself protected by the talisman of a wizard’s bauble. But when the Evil forces detect the company and mount a final assault against them, Duncan sees his only hope crumble in failure.He is left with only his courage and his mission . . .