This mission will only appear when you’ve completed 'Mexican Caesar', 'My Sister’s Keeper' and 'Must a Saviour Die?'
Reach the 'D' in the usual spot on the map however you please and when the mission starts you’ll be asked to head to Chuparosa. Ride shotgun with De Santa and you now have a choice: You can skip the ride with B/Circle or you can ride it out and take on the sharpshooter duel with De Santa’s men for a $25 reward (the choice is up to you).
Once you reach the town and enter, a cut-scene will play out. As soon as you regain control of Marston; run towards the right hand side of the building where the blue dot is on your radar. Head up the stairs towards Reyes and he’ll untie you.
Run back down the stairs and open the box by the centre of the town to get back all of your gear. Whip out your pistol and show those back-stabbing traitors what happens when you try and kill John Marston!
Use the circular fountain in the centre of town to provide excellent cover that also allows you to move quickly for a better shooting angle. Flank the building up ahead, and force your way inside with some close up executions and a good use of Dead Eye as well.
Equip your shotgun when you approach the front door and give the guy who bursts out a lead-filled welcome to the face. Clear the building from the ground floor up (taking your time and using all cover available).
When you reach the final door, you can either use your Dead Eye on the Captain, or you can show him real justice by getting up close and personal and triggering an execution animation. However you do it, you’ll complete the mission.