Juggler of Shapes

In a deserted street outside St. Savlons, the Care Home for Truly Disruptive Children, a stranger watches and waits…
 
“Humming softly under his breath, he took three black shapes from the pockets of his coat and one by one tossed them into the air, until all three were flying from hand to hand like bats in the darkness.”
Who is this mysterious Juggler? And what is the terrible danger that he brings to the children?
From the writer of Dragonfire comes the latest story of Polly and Courtleigh. Having escaped the clutches of the evil Lady Serena, they thought they were safe until…