Now that you are properly outfitted, Staelwyrn has a job for you.
This quest is only available if you started the game in Limsa Lominsa, you have completed the quest Dressed to Call, and have reached level 5.
Starting the Quest
Talk to Staelwyrn in Middle La Noscea to start the quest. There will be a cutscene.
Investigate Seasong Grotto
The next destination is in Middle La Noscea and will be marked on your map and minimap. The location is in a cave underground, so be sure to look for the slope leading down into the cave. The entrance to the cave is on the east side, between some mossy brick walls.
In the cave, you will find a Stone Monument. It has a glow around it, which means that there will be a battle sequence, also known as a Special Instance or instanced battle. Examine the stone statue for more information. You can also read about it in the Active Help window. If you don't see an Active Help window, you can go to the System Menu and choose Active Help, and search for Special Instances.
Before entering the battle, you will be prompted to Proceed or Leave. You can choose Leave if you want to wait and prepare first. Otherwise, choose Proceed when you are ready to battle. Note that you can try again, and can optionally lower the difficulty, if you fail the battle.
Solo Duty: Lurkers in the Grotto
After you click Proceed, there will be a cutscene. A tattooed stranger will assist you in the battle. Focus your attacks on the Frenzied Mossback while staying near the stranger, who will heal you as needed. After a while, two Bogys will appear in the cave entrance. Focus your attacks on these Bogys, but remember to stay near the stranger. There will also be some Frenzied Goobbues to fight, so keep focusing on killing these extra enemies. After you defeat the six extra enemies, no more will appear, so focus your attacks on the Frenzied Mossback from then on. After it dies, there will be another cutscene. This one is important, so if you've been skipping cutscenes so far, you might want to watch this one.
Deliver the Knife
After the cutscene, Staelwyrn will have a green checkmark over his head. Talk to him, hand over the knife, and there will be another cutscene. Afterward, you can complete the quest.
Next Main Scenario Quest
After completing the quest, you will need to be at least level 7 to proceed to the next quest. After you reach level 7, talk to Staelwyrn to accept the next quest: Washed Up.