Ordering freely from the standard menu of story elements, Crilley dishes up a Celtic-flavored fantasy featuring two (supposed) orphans in Victorian London who go up against any number of magical creatures with help from a good-hearted young thief, a smart-mouthed 2,423-year-old piskie and a secret society of humans led by Merlin and Christopher Wren. In this trilogy opener young Emily has to solve a riddle (“More riddles. Why is it always riddles?” complains the piskie) to find the hidden Key to Faerie, and then to keep it out of the hands of the Dagda and his consort, the Queen, lest they use it to bring their conquering armies into this world. Fortunately the Bad Guys like to explain their evil plans, and also some of the Faerie folk like the world the way it is; the climactic struggle leaves the key in Emily’s hands but sets up the next episode by casting her back to 1666 (the year of the Great Fire). A particularly resourceful heroine and some fuzzy lines between the sides set this apart (a little) from the crowd. (Fantasy. 11-13)