Now that you have killed Elpenor’s guards, you must begin the search for Elpenor himself. The quest description does not indicate any particular location, but the words of the Wolf prove useful here. 'Beware the snakes in the grass' can mean only one thing; Elpenor is hiding in the Valley of the Snake. The valley can be found to the east of Kirrha, and north east of Desphina Fort. When you approach the valley it will be revealed on the map, allowing you to locate the Snake Temple, where Elpenor can be found.
Be sure to synchronise with the view point south west of the Snake Temple, then make your way toward the temple. As you approach it, use Ikaros to scout the area and tag any enemies in sight. Once you have everything tagged, climb down the side of the cliff on which the temple grounds are located. From there you can whistle at the guards to draw their attention. When they are close enough, perform an assassination to throw themn off the cliff. You can do this for any guard within range to make the upcoming fight easier by reducing the overall amount of opponents. When there are no more guards within range of the cliff edge, climb up and crouch toward the nearest foe. Take note of your surroundings to ensure that you cannot be seen while you assassinate guards from behind.
When fighting any guards openly, keep in mind that heavy attacks will not always break their defences. The most effective way to do this is by using special skills such as Sparta Kick and Bull Rush, or by dodging their attacks and moving beside or behind them before performing a flurry of light and heavy attacks. When all the guards are dead loot the area and make your way inside the cave. There you will find Elpenor. Approach him to initiate the fight, and be wary of his swift attacks. He is more deadly than he seems. Focus on a flurry of attacks while keeping an eye on his movements, ready to dodge any incoming retaliation. When his health is low he will fall to the ground. You can now speak with him and watch a brief cut scene, at the end of which the quest will complete. Loot Elpenor and the cave before you leave.