Paid in Full is about a young man who rises to the top of the cocaine industry in Harlem. The protagonist, Ace, is played by Wood Harris. At the beginning of the movie, Ace is stuck in a dead end job working in a dry cleaner's shop. His sister's boyfriend, Calvin, is a big time drug dealer who often tries to lure Ace into becoming a part of the drug trade with promises of fast money and glamour. Ace resists these temptations, warning constantly that Calvin's flashy style and audacious method of dealing will get him arrested. When Calvin does get locked up, Ace ends up taking his position on the streets after a chance encounter with Lulu, a Dominican drug dealer. With the help of his friend, Mitch and their partner and enforcer, Rico, he creates a huge drug empire in Harlem. However - unlike most hustlers, Ace is careful not to draw too much attention to himself and stay, more or less, behind the scenes.
Mitch, Ace's best friend, is very popular and an extremely flashy drug dealer. Mitch does not pressure Ace to become a dealer because he thinks that his friend is not the hustling type. In fact, he humorously tells Ace that he will become the "George Jefferson" of the ghetto, making reference to his job at the dry cleaning shop. Eventually, Mitch gets arrested. During this time, though, Ace has been introduced into the drug game by Lulu. Soon after Mitch's release, Ace becomes partners with his best friend, realizing he cannot control such a lucrative empire on his own. The two quickly become successful, gaining a reputation worthy of street legends. Rico, a recently released inmate who came to Mitch's aid while Mitch was in prison, appears, and as a show of appreciation and gratitude, Mitch suggests to Ace that Rico join the team, since they could always use additional "muscle" to bolster their rise to the top. Ace agrees. The trio become extremely well known in Harlem, the center of their operations, as well as locations across New York, Washington D.C. and other areas. Ace, as always, tries to remain quiet with a low profile while Mitch returned to his image as the "rich, pretty boy" gangsta. Rico's reputation, however, is one of a ruthless 'killa' who is always quick to show his loyalty to Ace and Mitch by making an example of anyone who does not pull their weight on the streets.
After their rise, trouble soon finds them. When Calvin is released from jail, he tries to regain his position of power in the streets. After Ace gives him a lower-level role on the team, Calvin becomes dissatisfied with the thought of making money only as a result of Ace's generosity. Calvin cannot accept the idea of losing his former territory and clientele to Ace and decides not to partner with Ace if he cannot be one of the leaders of the team. He attempts to rob and kill Ace at his apartment one night and shoots him in several times, including a shot to the head. Ace survives, however, and begins to think it's time to leave the game before he is killed. Nonetheless, Rico kills Calvin in retaliation.
A short time later, Mitch's brother, Sonny is kidnapped. In an attempt to get his brother back, Mitch tries to raise the tremendous ransom the only way he knows how. He asks Ace, who is basically retired, to help him one last time to get a large quantity of drugs - enough to raise sufficient money to pay the ransom. Ace helps Mitch as requested. When Mitch reaches out to Rico for help to sell the drugs and raise the money, Rico takes this as an opportunity to establish himself and expand his hustle. He kills Mitch and takes the drugs Mitch intended to sell to rescue Sonny. Soon after Ace is told about what happened to Mitch, Ace realizes that Rico was to meet up with Mitch that same night and might be responsible for Mitch's death. Ace then sets up a meeting between him and Rico interrogating Rico on what happened between him and Mitch that night, Rico in return answers that he hadn't seen Mitch all day, Ace then realizes that he is lying and settles the score with Rico by giving him the number to two FBI agents working undercover as drug dealers that Ace had spoken to once before. Rico is arrested and is last seen in prison giving up information on his out-of-town connections in Washington D.C., but not on the connections he once had in Harlem, due to his is claim that "When I come home, I'm still gon' be the king." Since the ransom was not paid, Sonny is later found dead as well. Later, it is found that Sonny's kindnapping had been set up by his own uncle and was killed by Tommy an accomplice of their uncles who resented Mitch because he would not provide him with money. Ace does manage to get completely out of the drug game and makes a new life for himself and his family using diamonds he found in Lulu's apartment.