Fetch wants some help taking out some drug dealers, who she says has a big shipment at the marina. Head there and you will see that there are A LOT of enemies in the area. Don't worry about the boats for now and just concentrate on taking out all of the enemies. As you're fighting them, Fetch will likely pinpoint the exact location of three boats with drugs on them.
You need to go onto each boat, find the drugs and then tag the boat for Fetch to blow up later. On two of the boats, however, you will find someone trapped inside, so open the cabin door to let them out before tagging. When you get all three, Fetch says things are getting pretty hectic at the warehouse, so head there to find still even more enemies.
Once you take them all down, meet up with Fetch and watch as she destroys the boats. The mission isn't over, though, as they appear to be shipping one last shipment via a truck. You will have to follow this truck without being seen, so stick to the rooftops and follow Fetch. When the truck stops, take out the remaining enemies to finish the mission.
