After twenty-eight-year-old Lyft driver Erica Westfield learns her popstar sister is dead, the last thing she wants to deal with is a stupid hacker threatening to delete her sister's Facebook profile. Let alone a hacker who brings up Bloody Mary.

Since childhood, when Erica and her sister played the classic game of Bloody Mary one night, she has been haunted by the shadows Mary sent after her through the mirror. They're always nearby, waiting for the right moment to pull her through to a void somewhere far beyond the cosmos. Erica has tried to ignore them, but this hacker seems to know about them too. It turns out she's not talking to a hacker at all, but the lost spirit of a girl named Macy Abigayle, a lone wanderer who perished long ago on the Oregon Trail. Macy has been trapped within those same shadows Erica has been running from, within Bloody Mary's realm on the other side of every mirror, including Erica's computer screen. Bloody Mary sentenced Macy to relive the most traumatic moments of her life for eternity. Only Erica can help her escape.

To do so, Erica must race to the other side of Bloody Mary's mirror by facing the memories of her dead sister, including the ones she wishes she could forget. If she fails, all her remembrances of her sister will be lost-and she and Macy will be trapped within the mirror forever.