Irena Sendler was a humanitarian and social worker in Nazi—occupied Poland during World War II. Her job allowed her to pass through the armed gates of the Warsaw ghetto, bringing limited aid to the 450,000 Jewish people who were forcibly moved there. In secret, Irena built a network of people to smuggle 2,500 children out of the ghetto, saving their lives. And in a hidden jar, she kept their family names. This is her story.