Willful and outspoken Gabrielle van der Mal (Audrey Hepburn), the daughter of a prominent Belgian surgeon (Dean Jagger), leaves her upper-class existence to become a nun. As Sister Luke, she is eventually sent to the Belgian Congo, where she excels as a nurse working with a skilled doctor (Peter Finch). However, her willingness to continue as a nun is challenged when her father is killed by the Nazis, and she no longer feels that she can maintain the neutrality of her order.