"It is Princess Harriet Hamsterbone to the rescue when Heady the hydra's egg is stolen, but her search leads her to a castle accessible only by a rat with a very long tail"--
Wendell the iguana's dreams are all nightmares and a Dream Wasp wants him as a host for her eggs--so, with Great-grandfather Dragonbreath's help, Danny the dragon and Suki the salamander enter Wendell's dreams to try and defeat the wasp.
Not only must Danny and Wendell trick-or-treat with skeptical classmate Christiana, school bully Big Eddy dares them to enter a haunted house on Halloween night, where they may have to sacrifice their candy to a ghost.
"When Princess Harriet climbs an enormous beantalk, she finds an even bigger surprise--a giant rabbit is keeping a goose and a girl who is half-harp-half-hamster are prisoner, and it's up to Harriet to save the day"--