Recently laid off from his newspaper and desperate for work, Nick Bishop takes a humbling job: writing a profile of a new mindfulness app, Clarity. The app itself seems like a retread of old ideas – relaxing white noise and guided meditations. But then there are the 'Sleep Songs': a woman's hauntingly beautiful voice sings a ballad, but it's disturbing rather than soothing – more of a warning than a relaxation. However, it works. Deep, refreshing sleep follows.

As do nightmares. Vivid and chilling, they feature a dead woman who calls Nick by name and whispers guidance – or are they threats? Soon, her voice follows him long after the song is done. As the effects of the nightmares begin to permeate his waking life, Nick makes a terrifying discovery: no one involved with Clarity has any interest in his article. Their interest is in him. Because whilst he may not have any memory of it, he's one of twenty people who have heard this sinsister song before, and the only one who is still alive...