The "A Fine Time for It" Stranger mission in Red Dead Redemption 2 sees Arthur help an old man whose house has been claimed by some of the Night Folk. Before being able to start it, however, Arthur himself needs to have a run-in with these people and see with his own eyes how troublesome they can get.
The mission, however, requires players to experience a particular type of Chance Encounter that happens only in the Bayou region at night, so you may have a hard time initiating the mission if: (1) you don't often travel at night or (2) you usually ignore Chance Encounters.
The chance of this special type of encounter in the Bayou region is quite high, so you'll probably just need a single night-time trip to get involved in one.
The "A Fine Night for It" Stranger mission is available at any time from Chapter 2 onward, but to make Old Cajun appear on the map, you need to experience at least one Chance Encounter with the Night Folk.
There are two different possible encounters with them. The first one sees two Night Folk members dumping a body in a swamp, and Arthur can choose to simply witness the event, or kill the two men to loot their bodies for small rewards.
The second possible Night Folk Chance Encounter is a bit more lively. While traveling through the Bayou region at night, Arthur may hear a voice asking for help. Getting to the area marked on the map will trigger an ambush by members of the Night Folk. Killing them allows Arthur to loot their bodies for small rewards.
Once either of the two Chance Encounters has been completed, Old Cajun will appear on the map. He is located to the northwest of Lagras on the map, right to the south of the "B" in Bluewater Marsh. Old Cajun will only appear at night.
The Stranger will tell Arthur the story of how his house has been claimed by the gang and how needs help to get it back from them. Agreeing to help him will initiate the mission.
The "A Fine Night for It" Stranger mission is made up of a single part. Once Arthur agrees to help Old Cajun out, the old man will lead the outlaw through the swamp to his house. The way will be marked by bodies left by the Night Folk.
After a short while, Arthur and the Stranger will reach the house, where five members of the gang must be defeated. A full Dead Eye bar can help Arthur make short work of his enemies.
Once the Night Folk members inside the house have been killed, you can enter the house together with Old Cajun to claim your reward. The mission, however, is not yet over, as other Night Folk members will come out of the swamp to get the house back.
This fight is a little more complicated than the first one, as the enemies may disappear from the radar at any time to reappear close to Arthur. As they are armed with machetes, Arthur can die with just a few hits. To avoid this from happening, make sure to always stay on the move or find some decent cover that can protect you from these sneaky assaults.
Once the final wave of Night Folk has been defeated, the mission will finally be complete.