Trouble Finding Last Mission

[GM]

I have just finished the mission where you shoot the Russian guy at the airport but now I can't start the last mission. No one has phoned me up and there is no map icon for any missions.

Are there any requirements for the last mission exept finishing all the ones before it? I haven't done any side missions because I'm trying to get the Liberty City Minute trophy.

Thanks

 

[GM]

Don't worry.. thought ransom was a side mission not part of another mission.