A few months before her birthday, the world undergoes an unexplained phenomenon known only as "slowing", in which the completion of each revolution of the Earth on its axis takes drastically longer.

Crime rates begin to spike and people purportedly become more impulsive, the excuse Julia uses to convince herself when she finds her father having an affair with Sylvia.

Feeling lonely since Hanna's departure and her subsequent indifference, she strikes up a friendship with her long-time crush, Seth Moreno, and they eventually start a relationship.

Julia receives one last email from Seth after his reaching Mexico, but soon after, America is hit by a 72-hour black out because of excessive electricity usage to artificially grow crops.

Michiko Kakutani of The New York Times hailed the book as a "clever mash-up of disaster epic with sensitive young-adult, coming-of-age story" despite noting its "made-for-Hollywood slickness" and some wayward plot developments.

[2] In Entertainment Weekly Melissa Maerz agreed with Kakutani on the book's strengths, giving it an "A−" and praising it as "lovely, because of its simple writing and quiet moments.

"[9] NPR's Maureen Corrigan also enjoyed the book, writing: "The Age of Miracles is a pensive page-turner that meditates on loss and the fragility of both our planetary and personal ecosystems.".

[10] The Daily Telegraph critic Claudia Yusef focused on the emotional aspect of the book, opining that the slowing was "the basis for a startlingly evocative portrayal of the beauty and horror of adolescence" and that "quibbl[ing] with the physics, seems futile.

[12] Becky Toyne of The Globe and Mail felt the consequences of the slowing read "too much like a catalogue" and the narrator's refrain too repetitive, but nevertheless summed up the book as "touching and harrowing, but above all magical.