When you have reached Phokis, dock your ship in the harbour at Kirrha and then make your way to Elpenor. After a brief discussion with him two guards will appear. You will have to kill them, but Elpenor will be long gone before you have. They are fairly well armoured, so it will require a series of heavy attacks to break their defences, and make good use of your special skills.
Note: You will have to defeat the guards while other citizens look on. Try to avoid hitting them as this could raise the bounty on your head.
When the guards are dead, you can inspect Elpenor’s house for information. You will find notes to the left of the door as you walk inside, on the table in the centre of the room, and on the shelves to the right at the end of the room. When you have read everything, the quest will complete.