The last part of "The Reluctant Sorcerer". Trapped in a parallel universe, Dr Marvin Brewster marshals his renegade nation of brigands, dragons, trolls, vampire elves and the runesword Dwarfkabob, to challenge the evil wizard Warrick, who is playing the role of Destiny.
Simon Hawke (born 1951) is an American science fiction and fantasy author. He was born Nicholas Valentin Yermakov, but began writing as Simon Hawke in 1984 and later changed his legal name to Simon Hawke.
Simon Hawke. Wikipedia.