Hollow City (Miss Peregrine #2) by Ransom Riggs
Jacob and the rest of the peculiar children are on a mission to save their headmistress trapped in her bird form for time is running out. So they traveled from one time loop to another while being chased by the dreaded wights and hallowgast. I enjoyed it despite its rather bleak atmosphere. The ending left me hanging but not hopeless for finally Jacob realized the true real strength of his ability.