You can find Markos on the island of Kos, locked up in a nearby fort. Rescue him to start the questline.
You have a choice to either complete the quests and help Markos, or, refuse. Either way, you can still earn the achievement. To refuse (because screw you Markos), once you burn down the farm silos after sampling the wine, you can tell him he's on his own, ending the quest and unlocking this achievement.
If you want to finish the quest line, agree to help him to continue.