Skeleton Key by Piers Anthony

There's no dancing around a demonic threat in the fantasy world of Xanth in the New York Times-bestselling series.

 

Squid, the alien cuttlefish, is getting an upgrade: a boost to her shape-changing talent so she can lead a mission against a foreign Demon who's stirring up trouble in Xanth. At Squid's side are her rescued siblings and one very special child--Larry, a girl in a boy's body, who will act as a secret host for their adoptive mother, the Demoness Fornax.

 

Aboard the Fire Boat, they form a plan to disguise themselves as a traveling dance troupe. Each child is paired up with a native Xanthian. But it's the friendship that blossoms between Squid and Larry that will power their quest, and they'll have to do some fancy footwork to avoid the trials and tribulations that await them.