Game starts (credits scene) on an airport. Announcements being heard over the PA as we see, from the POV of the player, someone walking through the airport. As we get to the outside, a car is waiting for you. Man opens the door and you climb in. Camera then goes to some cinematic shots of the city (appears to be Los Santos) as you also hear a man sitting next to you. "Are you sure you want to go through with this"...yadda yadda yada. But you remain silent. Finally, you see the car coming into a parking lot and pulling up, Shot reveals it to be the Richards Majestic offices. Your character climbs out and it's revealed to be an older gentlemen in a suit. Next to you is some young kid in glasses, also wearing a suit, carrying a briefcase with him. He continues to talk to you as you continue to ignore him and walk into the office.
Next shot we see is of Michael DeSanta greeting you. He reveals that he is now the President of Richards Majestic after the death of Soloman Richards, who left it to you in his will. The man sits down and it's also revealed that this gentlemen, Mr. Carlucci, and Michael have a history together and worked with one another previously. Carlucci reveals that he's dying of cancer and wants to have his life made into a movie. And since Michael was once "in the life", he and his studio are the perfect ones to tell it and do it justice. The younger man with Mr. Carlucci is his attorney and keeps trying to butt in with demands but Carlucci tells him to shut up. Carlucci then tells his story:
Next scene is the 1970s in Liberty City. Carlucci was just a teenager then and was a street hustler. Selling bootleg cigarettes and doing some petty crimes (theft, robbery, stealing cars). Couple missions happen here with Carlucci and his partner stealing a cigarette truck and taking it to their hideout...and then a couple car theft missions. In the 4th mission, however, the cops are going to bust you for selling the bootlegged cigarettes and a foot race happens (maybe a few quick time mini games in dodging obstacles and leaping fences). You reach a point where you outrun the cops and then leap into an open window. It's revealed you've actually leaped into Studio 69...a parody of the famous nightclub in New York, Studio 54 and right into the women's dressing room. Of course you're discovered by a few of the goons and taken to the boss of the Club. The boss takes a liking to you and hires you on. So in a few missions you'll do a few "lookout" missions as well as a few shakedown missions for people who owe money. Also included will be more theft missions as well as delivery/retrieval missions for booze,drugs, women, etc (the better you do, the more options open up thanks to the "respect" feature that opens up more missions and unlocks hirer payouts and further features). Final mission will be that the club is getting ready to be attacked by a rival mob and it's up to you to hold off the invaders for as long as possible until backup arrives. During this mission, the boss gets shot and severely wounded. The backup arrives and then you have to take the boss to the mob doc. When you arrive, he'll tell you to get away and he'll make a few calls to get you some work. During a cut scene after this (with some belief that some time has passed since the shootout), he'll inform you that he has a friend who lives in Vice City and to pay him a visit.
Next chapter is....Vice City in the 1980s. This is around 1985. The family you're working for as ties with your Liberty City family but is more into the porn, gambling, and drugs side of the business. You're given the choice of what you want to be in charge of, but for the sake of this, let's say you chose to head up the porn side. So several missions will include recruiting girls for the business...running the stripclub/brothel, blackmailing politicians and cops who try to shut you down, and protecting the girls in case the johns get a little too rough among other things as well. As you progress, you'll also open up more side businesses (with the mob getting a certain percentage of the cut) as well as gain street cred (which helps in shooting, driving, etc...and can also lead to police being more lenient with you). Also as you do well with one side of the business, the family will open up more opportunities to you (allowing you to get a taste of the drugs and gambling sides as well). Last mission here will reveal that the Vice squad (Miami Vice) is getting ready for a huge crackdown on all your businesses (you get a heads up thanks to a connection you have in the department). So that mission will involve burning down/removing all incriminating evidence from your businesses and moving all assets out before the timer expires. After completing this, you take your assets that you've accumulated and you cash out and go to Las Venturas where you're told you'll be running a casino for your family (at this point you're pretty high up and start your own family but are connected to the original)
Finally we are in the last full chapter, Las Venturas in the mid 90s. Here, you'll be running a hotel/casino/nightclub so you'll be in charge of acquiring entertainment as well as other aspects of that. Several side missions here which will also include 3 or 4 huge heist missions to cripple rival casinos. Here, the final mission will be an FBI raid on the casino. Regardless of what you do here, you'll be caught at the end and sent to prison for tax evasion and a few other crimes (bribery, theft, etc).
Final scene is back at the studio where Michael is eager to start filming and agrees to make the movie. The attorney then interjects, decrying that Mr. Carlucci is not being paid enough and he demands more. Next scene shows the attorney "falling" out of the top floor office and hitting the concrete below. Carlucci says he trust Michael fully and walks off.
Just a rough outline I have...feel free to make any changes or add whatever you think would work. I welcome your thoughts/critiques/etc.