Charon: A Dragon at the Gate is a science fiction novel by American writer Jack L. Chalker, the third book in the Four Lords of the Diamond. First published as a paperback in 1982. It continues the saga started in Lilith: A Snake in the Grass and Cerberus: A Wolf in the Fold and is concluded by the fourth and last book called, Medusa: A Tiger by the Tail. Source: Wikipedia (en)