This mission begins at the question mark that is the westernmost in the Grand Senora Desert region. When you get there, you spot two men, one of whom speaks a foreign language. After the dialog, they tell you to get in the vehicle and drive to the Yellow Jack Inn.
Go inside once you get there and you notice no one unusual is inside. As you walk back to the entrance, Joe yells at you to get outside and back in the vehicle, as the guys he's after are getting away. Chase after the vehicles and if you can shoot their tires, do so. Otherwise, they will go off-roading. Once you stop them, shoot them both with the Stun Gun and that'll be the end of the mission.