Return of the Wizard — Kevin B. Shearer

England is once again beset with enemies from within and from without. But this time she faces a threat more deadly and savage than the NAZI scourge of WWII. It is at this unexpected time that Merlin chooses to return, and in a place and form just as unexpected. After selecting his last Guardian, a man of surpassing martial prowess, he trains him for their return to Old Blighty and to do what must be done.