Story
From the NES manual:
"As the last of the Line of Kings, only you possess the power to prevent the evil Warlock Lord from raising the Behemoth and unleashing it upon the land. Your quest lies within the Castle Shadowgate with its secret passageways, collapsing floors, and armed creatures. Your courage and wisdom will see you through... but a good sword might be helpful."
Long ago, there was a circle of twelve wizards. One of them, Talimar, fell to the lure of the dark arts and began lusting for power. Naming himself the Warlock Lord, he defeated all his peers, save for Lachmir the Ageless, and began preparations to summon the dreaded Behemoth. This terrible beast he would use for power, for dominion over the very world itself. Lachmir, unable to stop Talimar on his own, hid himself away and began searching the lands for aid. And he has found that aide in you, young Jair. It is up to you to make your way through the living castle of Shadowgate and save this realm from destruction.