The Bielski Brothers: The True Story of Three Men Who Defied the Nazis, Built a Village in the Forest, and Saved 1,200 Jews is a non-fiction book by Peter Duffy, which was published in 2003.
By using their intimate knowledge of the dense forests surrounding the towns of Lida and Novogrudek, the Bielskis evaded the Nazis and established a hidden base camp, then set about convincing other Jews to join their ranks.
In July 1944, after some 30 months in the woods, the Bielskis learned that the Germans, overrun by the Red Army, were retreating back toward Berlin.
[1] At the end of the war, with Soviet control of Belarus becoming increasingly oppressive, the surviving Bielskis fled to Romania, traveling on to the British Mandate of Palestine and eventually to the United States.
A novel telling a similar story would almost certainly be dismissed as outlandish, but Duffy's copious endnotes convincingly document the saga's reality.