Psychiatrist Sheryl Fleisch could be working in a posh office, rewarded with prestige and money. Instead, she's chosen to devote her life to the homeless.

Her patients live under the interstate highway in Nashville. Some are addicted to drugs. Some are violent. And many of them have mental illnesses, ranging from chronic anxieties to full-fledged psychoses.

As the creator and medical director of the Street Psychiatry Program at Vanderbilt University, Fleisch has a small operational budget and a cohort of medical students who follow her into the encampments, learning how to treat people at the bottom of society.

Lesson One: “Their tent is their home,” says Fleisch, “and you don’t just walk into someone’s home.” She begins by bringing socks, food, backpacks, bus vouchers, sometimes new tents.

The tent-dwellers test her until they decide she's for real. Then she’s invited in, becoming their physician, one they never have to pay. It’s a lifetime first for most of them.

That’s Sheryl Fleisch’s reward for giving up the safe, posh life she could have, anytime she might decide to stop taking her expertise and compassion into the tents under the highway.