Ten-year-old Annemarie Johansen is the main character in Number the Stars. The entire story unfolds from her perspective. Annemarie remembers a time before Nazis in polished boots occupied every street corner; she recalls "the music and the brightly colored lights, the carousel and ice cream" at the Tivoli Gardens. Throughout the book, she fears she won't have the courage to confront the Nazis. However, when tested, she instinctively acts with bravery.

The Johansens are a close-knit, loving family. Despite losing one daughter to the Nazis, Mr. and Mrs. Johansen continue to support the Resistance. Like the parents in many of Lowry's books, they are both loving and wise, which is evident in Annemarie's actions. Annemarie's five-year-old sister, Kirsti, is too young to understand the political situation and sometimes innocently reveals secrets, adding to the book's tension.

Ellen Rosen's father is a schoolteacher, and her mother is one of Mrs. Johansen's closest friends. When the Nazis announce plans to relocate Copenhagen's Jews, Lise's fiancé, Peter Neilson—who was injured during the raid that killed Lise—helps Ellen's parents go into hiding while Ellen stays with the Johansens, pretending to be their daughter.

One morning at 4 a.m., the Nazis, furious that the Rosens have vanished, arrive at the Johansens' house searching for missing Jews. When the Johansens try to pass Ellen off as their third daughter, the soldiers point out that Ellen has dark hair, unlike Annemarie and Kirsti, who are blondes. To address this, Mr. Johansen shows baby pictures of his three daughters, proving that Lise had dark hair as a baby. The Nazis reluctantly accept this evidence but maliciously damage the photos before leaving.

The next day, Mrs. Johansen takes Annemarie, Kirsti, and Ellen to her brother Henrik's farmhouse in the countryside. Uncle Henrik, a fisherman, has been secretly transporting Jews to Sweden, hiding them in a concealed compartment at the bottom of his boat. At the farm, Ellen is reunited with her parents, and that night, Mrs. Johansen guides the Rosens down a dark path to the waterfront.

Although the Rosens reach the boat safely, they forget to deliver an important sealed packet from Peter to Uncle Henrik. To complicate matters, Mrs. Johansen breaks her ankle and cannot carry the packet herself. Familiar with the path to the boat, Annemarie volunteers to deliver the packet to Uncle Henrik. When she encounters a group of Nazis with dogs, Annemarie feigns innocence and mimics her little sister's behavior. Despite her fear, she acts impatiently—just as she knows Kirsti would. As Peter planned, the Nazi dogs sniff the packet, which contains a scented handkerchief, and are thrown off the Rosens' trail.

It is only afterward that Annemarie learns the true importance of the scented handkerchief. When she hears that the Rosens have safely reached Sweden, she understands that every member of her family has shown immense bravery. "That's all that brave means—not thinking about the dangers. Just thinking about what you must do," she reflects. Annemarie, Uncle Henrik, Peter, and the whole Johansen family stand out as unforgettable examples of ordinary individuals ready to risk their lives for what they believe is right.