What if we could find cancerous tumors years before they can harm us -- without expensive screening facilities or even steady electricity? Physician, bioengineer and entrepreneur Sangeeta Bhatia leads a multidisciplinary lab that searches for novel ways to understand, diagnose and treat human disease. Her target: the two-thirds of deaths due to cancer that she says are fully preventable. With remarkable clarity, she breaks down complex nanoparticle science and shares a dream for a radical new cancer test that could save millions of lives.