More than a century after a catastrophic disaster wiped out most of humanity and covered much of the earth with ice, fifteen-year-old Cass yields to the voice in her head urging her to embark on a dangerous journey across a poisoned sea to the mythical land, Blue.

Miss Peregrine, Emma and her peculiar friends are back in Florida with Jacob Portman. They discover a subterranean bunker that belonged to Jacob's grandfather, Abe. Clues to Abe's double life as a peculiar operative start to emerge, revealing secrets long hidden in plain sight. Jacob begins to learn about the dangerous legacy he has inherited - truths that were part of him long before he walked into Miss Peregrine's time loop.