1: Speak to Brother Bert in the Septry near Fairmarket. He sends you to Fairmarket to speak to Elder Brother (located in the Castle).
2: Elder Brother gives you the task of recovering the relic (ring) of Baelor the Blessed from a group of bandits led by Aegon Bloodborn, outlaw son of Ser Aenys Frey, taking Aegon's head in the process. You're informed that Aegon is either hiding out around The High Fall or at The Crossing.
3: (Personally) Found Aegon Bloodborn at The Crossing in the Castle. Talk to Aegon and demand the return of the relic, then leave The Crossing.
4: This encounter spawns an army called The Outlaw of The Crossing consisting of 65 bandits located right outside The Crossing. They are fast (6.3 speed). These are Raider units and will have the traditional mix of horsemen, archers and infantry. Note: Killing Aegon himself is not enough to complete the quest, so make sure you bring enough men with you to wipe out their entire army.
5: After trouncing his army, Aegon may (probably will) escape. This is not critical to finishing the quest, simply return to Fairmarket and speak to Elder Brother and tell him you brought Aegon to justice. You are rewarded with 1,000 experience, 1 honor, a copy of The Seven Pointed Star (+1 charisma after reading) and -10 reputation with all Frey characters.