Action takes place during one day - 9.09.1944. This is a day, when Bulgaria goes out from Nazi coalition and join to antifascist countries. The supporters of Nazi regime are still fighting back. The partisan detachments are coming soon from mountains. The film`s young protagonist Mustafa is one of them. He will have to answer for himself important moral questions which the revolution asks of every man. He should decide for himself where exactly the boundary between justified and unjustified violence lies. This is a longest day in Mustafa life - the day of his coming of age. On this day he experiences his first doubt. Mustafa remembers a night when they had orders to kill a political instigator but his friend Matey has killed his child by mistake. Matey receives a light sentence but his guilty conscience makes him put an end to his life. Another young boy joins the troupe and receives his name. He acts without questioning orders and without displaying doubt.