Every 30 years, the small farm town of Aurora is washed in light from the Harmony Comet. Local legends say strange things happen when Harmony is in the sky: People disappear. They may even slip through time.

The comet is back this summer and Everly doesn't want to see it, because it’s just another promise her late mother made her, in a future that won't ever come now that she's passed. Then Everly meets the perfect distraction: fiery-haired and playful Sam, who likes 90s music and actual cameras and puts Everly at ease. When Sam vanishes just as quickly as she first appeared, Everly can't find any trace of her in the present. But somehow, she finds her in the past.

After accidentally stumbling back thirty years, Everly is thrust into 1998, where Backstreet Boys and dial-up internet reign, and nobody’s ever heard of a smartphone. A world where she’s falling head over heels for Sam, and where Everly meets someone completely unimaginable: her teenage mom. Everly needs Sam and her mom’s help investigating the comet’s legacy of missing people, since she’s supposed to be finding her way home –right? But soon, Everly exposes dark secrets and realizes she isn’t the first person to fall through time… and she won’t be the last.

Time may be malleable, but not every change is for the better. If Everly’s not careful, she’ll risk an altered future –one without her mother, or her dream girl.