What mission do you have to do to get to the thrid island in gta4

At the beginning of GTA IV, Niko Bellic arrives in Broker, and the island of Bohan is also available to him. The area of Charge Island, situated between Broker and Bohan is open as well. After completion of the mission Blow Your Cover, where Niko has to drive Playboy X back to his apartment in North Holland, the island of Algonquin is unlocked. This also includes Happiness Island, which is situated off Algonquin.

Some time after completion of the Three Leaf Clover mission, Packie will ring Niko and ask him to help out his brother Derrick. This will unlock the final island of Alderney, as Derrick is situated there.

All areas are then accessible.