True friendship is another major theme of Number the Stars. The Johansen family has a close friendship with the Rosen family. When the Rosens tell the Johansens that they have to go into hiding, the Johansens do not hesitate to offer their assistance because, "that's what friends do." The Johansen family risks their lives for their friends.
Despite the Nazi rule forbidding friendship between Jews and Christians, Annemarie and Ellen are best friends. Lowry portrays the characters as physical opposites — Annemarie is lanky and has blonde hair and Ellen is stocky and has dark hair — however, they enjoy each other's company immensely. In the beginning of the novel, when the Nazi soldiers confront the girls for the first time, it is clear that their friendship will be tested. Annemarie first proves her friendship for Ellen by yanking Ellen's Star of David necklace from her neck and hiding it in her hand so the German soldiers won't see it. Later, she risks her life when she takes the envelope that Mr. Rosen dropped to Uncle Henrik aboard his boat. All alone, she takes a path through the woods and is confronted by the Nazi soldiers. By acting like her younger sister, she is able to get the envelope with the handkerchief to Uncle Henrik. The Rosens and other Jews make it to Sweden and safety. Annemarie saves Ellen's life.
At the end of the novel, the war is over and Annemarie decides to wear Ellen's Star of David necklace, symbolizing her friendship with Ellen, until Ellen returns to claim it.
Lowry tells about the heroic acts of the Danes and portrays a deep friendship between Annemarie and Ellen that endures the oppression of the German soldiers to instill hope in readers for a world of human decency.
