Paris, 1940. On Armistice Day, seventeen-year-old Lili is caught by police laying flowers at the foot of a French hero's statue. This sets Lili on a path to come together with like-minded students, opposing German occupation. Meanwhile, a small group has joined forces to secretly produce a newspaper. Lili and The Kid undertake the dangerous job of distributing copies, and begin to fall in love.
Lili and The Kid narrowly escape being arrested by the Gestapo and discover there's a traitor in their midst. With nowhere else to turn they are forced to spend a night together at the only safe house they know, the local brothel. The next day, Lili undertakes another dangerous mission. However, her triumph is short lived when she returns to see Boris, their leader, arrested by the Germans.
Lili narrowly escapes capture by the Germans but this time, The Kid is not so lucky. Visiting him in prison, she doesn't know if she'll ever see him again. The Kid makes her promise to never give up the fight. Increasingly desperate Lili joins the Youth Battalion led by Fredo, a Communist who trains her to use guns, knives, and grenades. The Resistance movement becomes more violent.
Lili agrees to go undercover to transport a new resistance paper, “Combat.” Meanwhile, key members of the Youth Battalion are arrested, including Andre. The prisoners will be tortured and Lili is now in severe danger of being discovered. The young resistance fighters are tried and sentenced to death. Unexpectedly, and much to his fury, Andre is spared the firing squad, because of his young age.
Lili undertakes a daring mission to rescue Victoria from a mental hospital. But her efforts are short-lived when Victoria and other leaders of the Resistance are betrayed by the traitor and captured by the Gestapo. Lili witnesses the arrest of a Resistance member and this time recognizes the traitor. Taken to meet a key Resistance figure, she's amazed to learn who it is.
Lili makes a daring escape from the Gestapo and returns to Paris to learn that most of her friends have been killed or arrested. Lili and Jeannot are captured by the Germans in a cinema and brutally tortured. Sentenced to death, they're bundled onto a train bound for Germany. The Americans are advancing on Paris, but will it be too late for Lili?