Six months have passed since Arlo vanished, and Mars feels like they're the only person left who cares to find him. Marianne has locked herself away, Rani doesn't remember, and The Thorns have all but vanished. Nothing feels like it will ever be the same again. But time is running out. Whoever came for Arlo is close to their goal of a humanity defining event... one that must be stopped before it's too late. Arlo is not himself, he embraced the creature inside him and followed his new leader into the darkness. But he's also not alone. His father, whom he believed to be missing, is in the same situation as he is, and has been for a very long time. Will they be able to work together to fight the monsters within before they lose themselves forever, leaving the fate of humanity undecided? Secrets are revealed, pasts are uncovered and relationships are tested in the final instalment to the Fallen Thorns duology.