Josie Byrne's life is spiraling out of control. Her parents are divorcing, her boyfriend, Nick, has grown distant, and her physics teacher has it in for her. When she's betrayed by the people she trusts most, Josie thinks life can't get worse . . . until she starts having dreams about a girl named Jo every night at 3:59 a.m.
Jo's life is perfect: she's popular, her parents are happily married, and Nick adores her. Josie thinks she's just dreaming, until she wakes one night to see a shadowy image of herself in the bedroom mirror--Jo.
Josie and Jo are doppelgangers living in parallel universes that overlap twice a day at exactly 3:59. Fascinated, Josie jumps at the chance to cross through the portal and switch places for a day. But Jo's world is far from perfect. . . . Nick is not Jo's boyfriend, Jo's mom is missing, and at night, shadowy creatures feed on human flesh.
Josie is desperate to return to her own life. But there's a problem: Jo has sealed the portal, trapping Josie in this dangerous world. Can she find a way home before it's too late?