1. The Spark

Two Stanford graduates set out to disrupt the tobacco industry by creating a sleek new product for adult smokers but run into a series of struggles.

3. Where's My Juul?

Viral social media videos and word-of-mouth send Juul and its flavor pods flying off shelves — and into the hands of kids, causing nationwide outrage.

4. Overnight Billionaires

A landmark deal makes billionaires of Juul's founders but leaves other employees torn. A health crisis linked to vaping jeopardizes the company's future.