Mara Carlyle's senior year is going as normally as could be expected, until-wa-bam!-a fellow senior, Katelyn Ogden, explodes during third period pre-calc.
Katelyn is the first, but she won't be the last teenager to blow up without warning or explanation. As the seniors continue to pop like balloons and the national eye turns to Mara's suburban New Jersey hometown, the FBI rolls in and the search for a reason is on.
Whip-smart and blunt, Mara narrates the end of their world as she knows it while trying to make it to graduation in one piece. It's an explosive year punctuated by romance, quarantine, lifelong friendship, hallucinogenic mushrooms, bloggers, ice cream trucks, 'Snooze Button™,' Bon Jovi, and the filthiest language you've ever heard from the President of the United States.
Aaron Starmer rewrites the rule book with Spontaneous. But beneath the outrageous is a ridiculously funny, super honest, and truly moving exemplar of the absurd and raw truths of being a teenager in the 21st century...and the heartache of saying goodbye.