This mod adds some missions that you have to beat, it's not a total conversation. Don't forget to add the texture with IMGTool.

Missions:
Darkness Invasion:
Mission Start: Near Ryder's House
Mission Description: Sweet sends you a call alerting of some strange masked guys killing family members and tells you to go kill them. You must kill all the 5 masked guys and protect the family members they are fighting.
Mission Passed: Mission Passed if all masked guys are dead. You receive $10000 and respect. You also gain acess to the next Darkness Andreas mission (currently not maded).
Mission Failed: You fail if your homies die, you're busted or wasted.
Enemies: Darkness Disciples.
Difficulty: Easy.

See http://www.gtaforums.com/index.php?showtopic=364989 for more details.