Help Bonnie with the herd of cows during the storm in Red Dead Redemption before you can start this mission. Head to Mrs. MacFarlane, marked on the map with the letter B, and talk to her.
From the dialogue, we learn that Bonnie's father has mysteriously disappeared, and your task is to help the woman find him. According to her, the man went to inspect his property and was supposed to return. Mount your horse and follow Bonnie to search the ranch. After a short while, you will find him next to the corpse of a horse.
He found them already dead and believes it to be the work of the Dealers or Williamson's gang. Following Bonnie's father's orders, head to the ranch to arrive by wagon, but halfway there you will see a huge plume of smoke.
The burning building is the barn. Reach it, go around to the left, and climb inside using the attic.
Descend and unlock the barn doors to drive out the horses inside. Return to Bonnie and talk to her. It turns out the arson was the work of the same bandits. After talking to her, you will complete the mission and receive +37 points to the Fame parameter and +75 points to the Honor parameter.