Reach the point where the campaign icon is located on your map (you should have a Hideout point nearby that you can fast travel to, if you're otherwise a long distance away), then accept your mission.
Take out the convoy before it reaches Blume.
You need to destroy a convoy, just like the objective says.
From where you begin the mission, head across the street and pick up a vehicle. Then drive down to intersect with the yellow line on your map. You want to intersect as early as possible, to give you more time to mess with the convoy. The vehicles will be following the route indicated, starting on the right and headed left.
The main vehicle you need to hit is the armored truck. The other portions of the convoy matter very little. You can follow along and wait for the vehicle to pass near a steam vent. Then press the button indicated to neutralize it, if you have that ability. Otherwise, ram against the truck or one of the other vehicles in the convoy until you're noticed.
Once you have taken out the truck or convinced it to stop, its passengers will climb outside and you have to gun them down or run them down with your vehicle (the latter is especially nice, if you can do it, so you don't have to delay your escape at all). The target is easy to spot and usually emerges from the passenger side.
Kill all militia members or escape.
Getting rid of the target was just the beginning. Now you have to get out of the area without being killed. You should be an old pro at leading high-speed chases by now. Just use the same strategies as always. When you get away, the mission is done.
NEXT: Act III: The Future is in Blume