The Heir of Mistmantle (The Mistmantle Chronicles)

King Crispin and Queen Cedar have just had a baby daughter--Princess Catkin--and everyone on Mistmantle Island gathers for the joyful celebration of the Naming Ceremony.  But the day after, the princess suddenly disappears.  Urchin and all the brave captains are dispatched to bring back the princess, but come back empty-handed.  All clues point to Linty, an older squirrel who had gone mad with grief when two of her children had been culled during evil Husk's reign.  The islanders fall further into crisis as a mysterious illness takes hold and begins to spread.  There are whispers that perhaps Husk is still alive and seeking his vengeance.