After you clear the Serpent Reavers and their leader Denn the Orcatoothed out of Sastasha, Baderon sends you to Miounne, the Gridanian Adventurers' Guild leader.
This quest is available after you have completed the quest It's Probably Pirates.
Starting the Quest
To start the quest, talk to Baderon in the Drowning Wench in Limsa Lominsa.
Speak with Miounne
Go to Gridania and talk to Mother Miounne in the Carline Canopy to complete the quest.
Next Main Scenario Quest
After you complete the quest, you will need to be at least level 16 to proceed to the next quest. After you reach level 16, talk to Miounne to accept the next quest: Fire in the Gloom.