The LAST mob, DROPS a map piece you have to pick up and read and hail Jack AFTER mission is done, then click map to get a path to where the chest is hidden. Thats is if you managed to kill the last mob fast enough and he didnt have time to burn the map, then you will loot a worthkless, burnt map.
Completely the wrong quest, but thanks for the input. This is the one for the Horn of Unity, not the Shimmering Black Pearl.
If one mob got past you and zoned it is a fail for the horn. You can still win but you don't get the bonus item.
