If you’re playing blackjack the way most people do, experts say you’ll lose about $4 for every $100 you put in. Luck varies wildly from hand to hand, but if you play long enough, that’s said to be the average.

Counting cards takes some quick mental math and a fair amount of subterfuge, but it can give you a slight edge if you bet big and play a lot. One study found that after thousands of hands, with a perfect strategy, you could win $50 for every $100 bet.

That’s a big difference, but is that enough to make a career out of gambling? As an aimless grad student, Roze Travis joined an underground card counting team. It was a ragtag group of people who found a community in a risky side-hustle.

In just a few months, Travis was taking on new identities, traveling the country and hoping to win big. When her team’s most important player was barred from a casino, she was forced to step up.