This is the final main story mission, which can be accessed after the mission "Cap The Collector".
Tommy visits Rosenberg and Lance. Rosenberg, as ever, is panicky with the Forellis bearing down on them. Lance gives the proper low-down, telling Tommy that Sonny is not happy that their collectors were taken out. They are arriving in Vice City to take their cut from the busted deal. Tommy wants Sonny and his family to see that his criminal empire is his ONLY, and orders Rosenberg to get the first batch of counterfeit notes to pay them off. He then orders Lance to round people up.
Tommy, Rosenberg and Lance are greeted by Sonny Forelli, jokng about Tommy's jail sentence. This brings up some cold feelings, before the counterfeit money is handed over. However, a rat is uncovered - Lance has sold Tommy out, and plans to take his place when Sonny takes over. He also tells them the location of Tommy's money. The final showdown begins.
You have to protect the safe before you have a shot at taking down Lance. He will stop a few times at the corridor leading to the staircase, and then you will have to take him down at the top level. Take the Adrenaline Pill up here, and take out Lance and his bodyguards. You have to head downstairs, and face off with Sonny himself.
Before doing that, head down to the bottom of the staircase and take the Health and Armor before facing him off. Concentrate on Sonny alone, as he is the most powerful out of his guards. When he is dead, you are done.
Tommy and Rosenberg contemplate the aftermath, and Tommy declares that he has full power over Vice City and the Forellis up north. The credits roll on Vice City, and the storyline has ran its course.
Mission Passed: $30,000
Congratulations. You should have completed the storyline upon doing this mission.