This book of fantasy is about a crippled Irish lad of sixteen, who finds a magic emerald belonging to the Great Lord Murdrun. As compensation for its return, the Great Lord promises a cure to Sean's infirmities. Shortly after the return of the gem he meets a beautiful fairy princess who asks him to accompany her to the land of McCush for the purpose of aiding her father, the good King of McCush, in the defeat of the evil King of McDonnaland.
Once in the land of McCush, Sean becomes strong and healthy and, with the aid of the good King's high council, learns how to have his spirit leave his body and travel anywhere.
Sean eventually defeats the evil king and marries the princess.
Complications arise and Sean is snapped back to his own dimension at the exact time he left. Thinking that his visit to McCush had been only a dream, Sean fmds around his neck an amulet that had been given to him by the King.
Unable to return to McCush during his lifetime, Sean spends the rest of his life in solitude, until the day he dies, when he is returned to McCush.