Suzy and Nancy Goodman were more than sisters. They were best friends, confidantes, and partners in the grand adventure of life. For three decades, nothing could separate them. Then Suzy got sick. She was diagnosed with breast cancer in 1977; three agonizing years later, at 36, she died.

It wasn't supposed to be this way. The Goodman girls were raised in postwar Peoria, Illinois, by parents who believed that small acts of charity could change the world. Suzy was the big sister - the homecoming queen with an infectious enthusiasm and a generous heart. Nancy was the little sister - the tomboy with an outsized sense of justice who wanted to right all wrongs. The sisters shared makeup tips, dating secrets, plans for glamorous fantasy careers. They imagined a long life together - one in which they'd grow old together surrounded by children and grandchildren. Suzy's diagnosis shattered that dream.

In 1977, breast cancer was still shrouded in stigma and shame. Nobody talked about early detection and mammograms. With Nancy at her side, Suzy endured the many indignities of cancer treatment, from the grim, soul-killing waiting rooms to the mistakes of well-meaning but misinformed doctors. That's when Suzy began to ask Nancy to promise: to end the silence, to raise money for scientific research, to one day cure breast cancer for good. Big, shoot-for-the-moon promises that Nancy never dreamed she could fulfill. But she promised because this was her beloved sister. "I promise, Suzy... even if it takes the rest of my life."

Nancy soon found a useful outlet for her grief and outrage. Armed only with a shoebox filled with the names of potential donors, Nancy put her formidable fund-raising talents to work and quickly discovered a groundswell of grassroots support.

Promise Me is a deeply moving story of family and sisterhood, and a soaring affirmative to the question: Can one person truly make a difference?