"In need of capable fighters willing to hunt down deserters in Fodlan's Locket."
"A soldier has obtained information about the deserters. It seems they are skilled soldiers, so you should persuade them to join you."
Quest-Giver Dialogue 
"Some soldiers stationed at Fodlan's Locket abandoned their posts. They weren't what you'd call upstanding folks. It would be a real headache for us if they became bandits and started wreaking havoc in the towns."
Quest Completion Dialogue
"I heard that you handed a crushing defeat to those Fódlan's Locket deserters. Sounds like, after your little intervention, they've changed their tune and are back on our side. Thanks for keeping 'em in line."
Given to you by a female soldier dressed as an archer near the back end of the Entrance Hall.
Subjective: The following part of this article is based upon the editor's personal experiences and opinions, and therefore may not be applicable for all readers.
Talk to the soldier at the far end of the Entrance Hall and accept the quest on the player's next day off.