In A Visit From Merlin, George Valentine receives an intriguing case from Arthur Thurston Renwick, a collector of medieval art. Renwick's world is one of eccentricity and obsession, filled with treasures from the past, but it is also haunted by a mysterious figure who has been appearing at his castle, Renwick Manor. This stranger, described as a little man in a tattered coat, presents a chilling presence, especially after he hands Renwick a bloodied 10th-century dagger that has gone missing from his collection.