Harper McKenzie wakes to the worse possible day: her 18-year-old son has vanished from her Manhattan apartment without trace. Worse, no-one knows what she's talking about. No-one thinks she had a son. Ever. Has she lost her grip on reality? Or has the world shifted in a terrifying and unpredictable way? The Effect is a taut psychological thriller that challenges everything we thought was real, as Harper's quest to find her son pushes her to the very edge of reason.