Kate O'Hara’s daughter, Rosie, is one of a small percentage of children with a disorder that prevents them from being immunized. All Kate can do is hope that herd immunity keeps disease at bay and her little girl safe. For Madeleine Cooper, vaccinations were a leap of faith she wasn't prepared to take. Following much soul-searching, she and her husband declined controversial measles shots for their daughter, Clara. But when both girls wind up in the same elementary school class, telltale red spots appear on Clara's chest, and on Rosie's a few days after. And while one child recovers and the other's health becomes more critical, the two mothers find themselves across a very deep divide.