Uncertain Magic is in the tradition of such classics as The Narnia Chronicles, and the books of Edward Eager and Lloyd Alexander.  It is set in the Kingdom of Pandium, on a tree-covered island in the midst of a vast ocean.  In Pandium magic is an art that those who are gifted and trained can master.

The story involves four children.  Nat and Katie are ordinary kids who live in the Florida Keys.  They are ten and twelve, and brother and sister.  Kyp and Edwin live in Pandium, and are both about eleven years old.  Edwin is Crown Prince, and will become King on his upcoming birthday.  Kyp is an apprentice to the Royal Magician, Krisgen, but is really more like a slave than an apprentice.

Kyp overhears Krisgen plotting to kill Edwin, and warns the prince.  Together they hatch a plan to use one of Krisgen's spell books, and Kyp's uncertain magic, to summon a hero capable of defeating the conspirators.  But instead of a fierce, enchanted warrior, they instead conjure Nat and Katie, two ordinary and very unwarrior-like children.

Now stuck in Pandium, Nat and Katie have to work with Kyp and Edwin to defeat the wizard,  Only when Edwin is safe can they hope to return home.