What mission in gta 4 do you unlock alderney?

You unlock Alderney by completing "Three Leaf Clover". The last of Packies missions.

Amazing mission by the way. It is not every day you get to rob a bank...I recommend saving before you do it and saving a backup so you can play it again. It's fun.

You may need to finish all of F McReary's missions too. His last mission is "Lure"

I finished all missions except for "three leaf clover" and that was the last mission i could do. I did it and Alderney opened up.