Fighting Fantasy: City of Thieves by Steve Jackson (author) and Ian Livingstone (author)

Terror stalks the night as Zanbar Bone and his bloodthirsty Moon Dogs hold the prosperous town of Silverton to ransom. YOU are an adventurer, a sword for hire, and the merchants of Silverton turn to you in their hour of need. Your mission takes you along the dark, twisting streets of Port Blacksand to seek the help of the wizard Nicodemus. But Blacksand is riddled with thieves, assassins and foul creatures. Should you survive, you must journey to the most terrible place of all – the tower stronghold of the Night Prince himself, Zanbar Bone!