In Desert and Wilderness — Henryk Sienkiewicz

In Desert and Wilderness is a popular novel for young people by Polish author and Nobel Prize-winning novelist Henryk Sienkiewicz, written in 1912.
It is in fact the author's only novel written for children. It tells the story of two young friends, Staś Tarkowski and Nel Rawlison, kidnapped by the rebels during Mahdi's rebellion in Sudan.
It was adapted to cinema in 1973 and 2001.