Note: Before you begin this quest, make sure that you go to the bandit camp to get the wood for Drucilla. Kill the bandits and bring the wood back to her. You can then find Markos to maximise your reward.
Markos is now relocated to a position north west of his vineyard. Use Ikaros to discover his precise location.
Once you have Markos tagged, go and speak with him. He will discuss the details of a plan to acquire enough drachmae to pay back the Cyclops. Incidentally, the plan to repay the Cyclops also involves stealing from him. Your task is to infiltrate the Cyclops' Lair to find and steal a valuable obsidian eye, inlaid with gold. The lair can be found to the north west of Markos' vineyard, as seen below.
As you approach the lair you will note that there is a high concentration of thugs. To avoid wandering aimlessly among many opponents, use Ikaros to scout the area and identify the precise location of the eye. Once you have it your character will acknowledge it verbally and you can make your way through the most direct route.
Note: When you approach the house you will see that the entrance is heavily guarded. It will be difficult to kill each guard without being seen in this current formation. Instead, you should find those thugs which are viable for assassination without being seen. As you clear the lair in this way, more thugs will move around and the formations will disperse, allowing you to take out each guard as they roam.
Once all the guards are dealt with, you can enter the house and steal the obsidian eye. You will find it in a white pouch atop an ornate table. Alternatively, you can make your way into the house without killing any of the thugs by jumping on the roof of the house and then stepping down at the entrance, leaving the same way you entered. However there is stil a risk that you will be caught and even if you are not, this method provides significantly less loot without killing the thugs.
Whatever method you choose, once you have the obsidian eye, take it back to Markos to complete the quest.