When you have these items, visit the statues in front of each of the Towers of the Four Spirits in Placid Plain. At the towers, there will be a shadow on the ground in front of the statue. Click it to start the fights.
FIGHT: At the first three towers (North, West, East) you will be unsuccessful at your attempts to find Larry and will attract the attention of 3 Byway Bow-Wows (level 20 non-elemental Commoners) that you must defeat within 20 minutes. You'll receive 5600 experience points at each tower.
FIGHT: When you start the quest at the Southern Tower, you'll see a cut-scene. You then have 20 minutes to defeat the Dreamdasher (level 25, Water, Martial Artist, 84,149 HP). Receive a Rib of Ruin and 11200 experience points.
Return to Old Man Shaun during the hours he is available. You need to bury the Rib of Ruin at the Southern Tower but you must have a Slow Hoe on hand (closest place is the Farming Merchant at X:197 Y:487 who will sell one for 200g). Return to X:393 Y:621 to dig.
After the cut-scene, you will receive your rewards.