Blue Noon by Scott Westerfeld

In this concluding installment of the Midnighters trilogy, a tight-knit group of teenagers in a small Oklahoma town who can access a hidden “secret hour” at midnight face a frightening escalation as that hour begins to leak into daytime; with the sinister creatures of the secret hour growing more powerful and unexpected betrayals and losses testing their bonds, the teens race to understand the phenomenon and stop the invasion before the normal world is consumed, confronting hard choices, sacrifice, and the consequences of meddling with time.

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