Just because you're paranoid, it doesn't mean they're not out to get you. Conspiracy theorist Miles Mokri is shot on the very best day to be shot: Miracle Day. He doesn't die, but he is silenced, and his survivors are left only with cryptic clues he left behind. His sister Holly and friend Nick team up to decipher the clues and find out what Miles knew about a mysterious "Key," one of the secrets of Miracle Day.

During the frantic search for the Key, Holly, a cancer survivor, is faced with new enemies, betrayals, and mysterious references to something called "Torchwood." By the time she uncovers the Key, she's learned something about it that may change her mind about everything, including the Miracle itself.

In a parallel story, back in 2007, Gwen Cooper and Jack Harkness live out a harrowing "missing day" that twines around Holly's story and fills in a missing chapter in the history of the Miracle that changed humanity.