Mostly for Polish viewers, some basic knowledge of 17th century Poland may be helpful if you want to understand the movie. It's about the rebellion of Ukrainian Cossacks against their lords - Polish nobility (it was before tsars conquered Ukraine). Polish prince Jeremi Wisniowiecki fights them with extreme atrocity but when they ally with Tatars, is forced to withdraw to the fortress of Zbaraz. These events form a background for the love between one of Polish commanders and girl he meets while carrying out some emissary mission for the prince. The movie is based on the novel "With Fire and Sword" (orig. "Ogniem i mieczem") by Henryk Sienkiewicz (Nobel award for "Quo Vadis"). This book is the first part of a trilogy, other parts have also been filmed. I think it's important to read the novel and see all mentioned movies - "The Deluge" (orig. "Potop") and "Pan Michael" (orig. "Pan Wolodyjowski").