The PC:s get kidnapped in their youth, before starting their career as adventurers. (This of course makes it difficult for the players to choose a scholarly profession, but it is not impossible.)
The kidnapper (in our campaign his name was Barbarossa) is really a slaver who enjoys tormenting his captives before selling them off in a slave market in a country faaar from the respective PC:s home.
After x years of slavery in {a coal mine, a salt mine, the fields picking cotton} our heroes get a chance to escape. The escape can be an adventure by itself.
The PC:s may be from any part of the world. (They may even have problems in understanding each others language in the beginning.) After successful escape they by incident see Barbarossa. The word "revenge" suddenly appears in their minds.
What can they do to hurt the seemingly too powerful slaver?