Summer 1944. Polish armed forces are being organized in the Lublin region. Edward, one of the generals of the First Army, receives an order to form an artillery division. He counts on the help of Stefan, his old friend who lives in Lublin. However, it turns out that Stefan - a colonel and commander of the Home Army during the occupation - was arrested...

Marta comes to Lublin as a captain of the Polish Army. She is looking for information about her son - Stefan, whom she last saw years ago, when she went with her husband to fighting Spain.

The film is based on true events. Officers locked in a POW camp make a desperate attempt to get out. A group of daredevils undertake to dig an underground tunnel through which they can escape. We learn about their moral dilemmas, solidarity and loyalty to their friends. This is especially emphasized in the last scenes of the film.