Toadling is a changeling—a child who was stolen from her cradle by wicked fairies less than an hour after birth and replaced by their own daughter. The fairy’s family don’t care what happens to Toadling once she’s in their realm, but luckily she’s adopted by a clan of river-dwelling “greenteeth” fairies. These beings—who have sharp green teeth, green skin, and algae-like hair—treat Toadling as one of their own and teach her some of their magic, most notably the ability to turn into a frog at will. 

When Toadling is about eight, she’s whisked off to live with ordinary fairies. These fairies have a greater range of magic than do the greenteeth; they’re able to work with the other elements and to cast spells under certain conditions. The fairies are generally capricious and cruel, and treat humans as their playthings. But some fairies, including the ones Toadling studies under, disapprove of that practice, and attempt to protect humans when they can. They prepare Toadling to protect the household she was born in from the fairy who took her place in it.