Young adult fiction is under no obligation to be gentle, and When All the Girls Are Sleeping takes the exemption. The title does its atmospheric work before the story starts, all night-time and sleep and the implication of somebody awake inside it, which places Emily Arsenault at the darker end of the teen shelf rather than its reassuring one.
Length is the second signal. At over twelve hours this is a full-scale novel rather than a quick young adult read, with the space that implies for backstory, misdirection and a slow accumulation of dread. We hold to what the recording supports, and the recording supports a writer content to take the long way round.