Back To Church
Father Ned has had Confessional with a guy that admitted to fencing diamonds. Usually whatever's said in there stays in there, but not this time. The handover is at Rockport Ferry Terminal, and you need to retrieve those diamonds.
The Lord's Dirty Work...Act 2
Get to the terminal. Be careful, though - these guys pack a massive punch when all of them set their sights on you. Kill them all, one by one, grab the RPG and take down the chopper. Retrieve the diamonds and take them to Liberty Tree Offices.