Young Indiana Jones and the Ghostly Riders is a 1991 novel by William McCay, part of a series focusing on famed archeologist Henry "Indiana" Jones, Junior in his younger years. This book in particular draws much inspiration from Arthurian legend.
Plot[]
While on a visit to Wales, 14-year-old Indiana Jones is sent many centuries back in time, to the period following the fall of Camlann (Camelot) and the death of High King Artorius (Arthur). He comes across ghostlike riders, which include Morgen, a woman well versed in magic who helped Queen Gwenhynfar (Guinevere) escape. He later ponders how Morgen became know as the villainous Morgan le Fay although she fought on the side of good.