A mysterious hospital deep in the Oregon woods is sending marauding ambulances into the countryside, looking for new patients. Mowing down anything in their path, the deadly ambulance drivers have forced the people and animals of the land into hiding. Twelve-year-old Chloe Ashton has returned to Fairfax and is desperate to find her mother. Together with her friends—the magical cook Mrs. Goodweather, carpenter Brisco Knot, and clever white rat Shakespeare—she hatches a plan to enter the hospital and stop the bloodshed. At the same time a rumor reaches them from the east: Silas the Stargazer is coming, and he is bringing an army. An animal army.