Heroin

Heroin is an illegal drug that is a plot element in Grand Theft Auto IV, The Lost and Damned and The Ballad of Gay Tony. Like the diamonds, it also has a large part of the game that involves the protagonists Niko, Johnny and Luis.

Changing Hands
When the Platypus arrived in Liberty City, the heroin, which belonged to the Triads and brought in from the east, was smuggled into the city together with the diamonds and Niko Bellic. The heroin was stolen from the Triads by The Angels of Death to sell it on the streets but the Angels soon lose it when Johnny Klebitz and The Lost Brotherhood destroy the AoD clubhouse and steal the heroin for themselves. Through Elizabeta Torres, The Lost try to sell the heroin, along with Niko Bellic and Playboy X as supervisors but the deal turns out to be an LCPD sting. Johnny escapes with the heroin and takes it back to the Lost MC clubhouse while Niko and Playboy escape empty-handed.

The Lost MC decide they will try to sell the heroin back to the Triads. Johnny, Billy Grey, Jim Fitzgerald and Brian Jeremy all go to the heroin deal which was actually a trap set up by the Triad Leader and Billy to kill Johnny and Jim. The hit fails and Johnny and Jim escape while Billy is arrested by the LCPD and the Triads regain their heroin. On a side note, Luis Fernando Lopez and Tony Prince had previously met with the Triad leader (after he spoke with Billy Grey about killing Johnny and Jim) to discuss some licensing arrangements for the planning department on behalf of Rocco Pelosi.

Phil Bell, an associate of the Pegorino Family hires Niko Bellic to ambush the Triads and steal the heroin before they can offload it. Niko hijacks the truck containing the heroin and takes it to an abandoned house in Westdyke, where Phil's nephew, Frankie Gallo will "sit" on the product until it is safe to sell it. After some time, Niko and Phil go to the house to move the heroin, however, the house is being monitored by the FIB. The three of them fight off the FIB and NOOSE before hiding the heroin again in a house in Leftwood.

Eventually the boss of the Pegorino Family, Jimmy Pegorino, makes a deal with the Russian Mafia head Dimitri Rascalov, joining forces. Pegorino gives all the heroin to Dimitri to sell it to Ray Bulgarin and asks Niko to accompany Phil when overseeing the deal. Niko is reluctant due to his personal grudge against Dimitri, but Jimmy attempts to persuade him otherwise. However, Niko is again left unsure when his cousin Roman and girlfriend Kate advise him in opposite directions, with Roman urging him to do the deal and Kate telling him to cut his ties with Dimitri altogether due to his previous betrayal.

Niko then either takes Revenge or does the Deal.

Deal
If Niko does the deal, Dimitri betrays Bulgarin by killing his men who were acting as buyers and keeps the heroin, claiming he doesn't wish to sell it at such a price. He then informs Niko and Phil of this, leaving them to the mercy of the men who were supposed to give them the money. However, Phil and Niko kill the men and steal the money. Dimitri sends a hitman to kill Niko at Roman's wedding, but Roman is killed instead during the struggle. In retaliation Niko pursues Dimitri and Pegorino to an abandoned casino in Alderney. There, Dimitri betrays Pegorino and kills him in another act of betrayal (mentioning that he "did not work that hard to share the spoils of a victory") before escaping by helicopter. Niko, now ready to finally end things with Dimitri once and for all, chases him in a helicopter provided to him by Little Jacob and corners him on Happiness Island after both their helicopters go down. There, Niko injures Dimitri and confronts him about what he's done before shooting him repeatedly and watching him succumb to his wounds.

Revenge
If Niko chooses to take revenge, he goes to the Platypus, where Dimitri is hiding and storing the heroin, and carries out a full-blown assault where he kills Dimitri and his men. After killing Dimitri, Niko leaves the scene, and the heroin is left on the ship.

Niko's revenge leaves the Pegorinos ruined, with neither the money or the heroin. Niko then attends Roman's wedding, but Pegorino intervenes and tries to kill Niko by firing on the guests, though Kate McReary is killed instead. Days later, after tailing some of his goons to a meeting, Niko finds Pegorino hiding in an abandoned casino in Alderney. When confronted, Jimmy tries to escape on a boat, but Niko follows in hot pursuit. After a lengthy chase through land, sea and air; Niko kills Pegorino on Happiness Island.

The Destruction
With both Dimitri and Pegorino dead, Bulgarin steals the heroin, which had been left in storage aboard the Platypus, and stashes it away in Funland. However, Luis Lopez goes there in pursuit of Bulgarin and ends up in a large shootout against Bulgarin's crew. Ultimately, all of Bulgarin's henchmen (as well as his right-hand man, Timur) are killed and the heroin is destroyed. Bulgarin himself is soon after assassinated by Luis when he tries to leave Liberty City via jet.

Niko Bellic
After the Triads take back their heroin, which they believe is cursed, they later attempt to ship it. The Pegorino's hear about this and so Niko, under orders from Phil Bell, steals the heroin and hides it in an abandoned house. When Niko and Phil go to pick up the heroin, the FIB attempt to bust them. After they escape the FIB and NOOSE, the Pegorino's ally with the Russians and try to sell it to another Mafia Family. Pegorino gives the heroin to Dimitri, who says he has found a buyer. But Dimitri kills the buyers and steals the heroin for himself in the "Deal" ending, while in the "Revenge" ending he never gets a chance to try and sell it due to Niko's ambush on the Platypus.

Johnny Klebitz
Johnny and the Lost MC steal the heroin from the Angels of Death clubhouse, unaware that the Angels of Death had stolen it from the Triads to begin with. First, Johnny arranges for Elizabeta Torres to help him offload it. Elizabeta uses Playboy X and Niko Bellic to oversee the deal. However, it turns out to be an LCPD sting, the three of them escape, and Johnny takes the heroin back to the Lost MC clubhouse. When the Lost MC discover the heroin belonged to the Triads, Billy sends Jim and Johnny to sell it back to them. However, it is revealed that Billy arranged for the Triads to ambush and kill Johnny when he arrived. Johnny and Jim survive the ambush, however, and the Triads take back their heroin. In the meantime, the cops show up and arrest Billy, and Johnny does not see or hear of the heroin afterwards.

Luis Lopez
After Dimitri was killed, Luis destroys all of the heroin, and kills Bulgarin soon after. In "Deal", Luis does this immediately after Dimitri's death on Happiness Island. In "Revenge", Luis does this at some unknown time after Niko kills Pegorino.

Prominent Appearances in Missions
Note the following missions are sorted in chronological order of the timeline.
 * The Cousins Bellic (GTA IV) - Appears being loaded into a Schafter by the Triads.
 * Action/Reaction (TLAD) - Stolen by Johnny Klebitz, Billy Grey, and Brian Jeremy from their rivals, the Angels of Death.
 * Blow Your Cover (GTA IV) and Buyer's Market (TLAD) - Elizabeta Torres gets Niko Bellic & Playboy X to supervise Johnny Klebitz during a deal with a stranger. The deal turns out to be a sting by the LCPD, but Johnny, Playboy and Niko all escape.
 * This Shit's Cursed (TLAD) - Johnny Klebitz and Jim Fitzgerald try to sell the Heroin back to the Triads, only to have it stolen. They escape the building, killing many of the Triads in the process, only to discover that Billy Grey has been arrested. In TBOGT, it is revealed that Billy originally set up an ambush with the triads to kill Johnny and Jim; but he failed to account for the police.
 * Truck Hustle (GTA IV) - Niko Bellic, on the orders of Phil Bell, steals the Heroin being held by the Triads and sends it over to Frankie Gallo.
 * To Live and Die in Alderney (GTA IV) - Niko and Phil go to collect the heroin, only to discover that Frankie was under surveillance by the FIB. After a lengthy chase around Alderney and a shootout with NOOSE, Niko, Phil, and Frankie deliver the heroin to an apartment in Leftwood.
 * If the Price is Right (GTA IV; Deal) - Niko discovers the Heroin he thought he was dealing was stolen by Dimitri Rascalov, forcing him and Phil to fight through the buyer's warehouse to steal the money. They kill all of the buyers and leave with the money.
 * A Dish Served Cold (GTA IV; Revenge) - Dimitri is supervising the Heroin shipment on the Platypus, but Niko launches an attack on the ship, killing many of Dimitri's goons and Dimitri himself. With Dimitri gone, Ray Bulgarin claims ownership of the heroin.
 * Departure Time (TBOGT) - After destroying the heroin and killing Timur at Funland, Luis Lopez rushes to the airport with Yusuf Amir's help and kills Ray Bulgarin aboard his private jet.

Trivia

 * The Heroin, like the Diamonds, are a key part of the Pegorino Family's missions; Ray Boccino operates with the Diamonds while the others operate around the Heroin.
 * With the exception of Niko, Luis, Elizabeta (who ends up in jail), and Phil, everyone involved with the Heroin dies; this includes Billy Grey, Brian Jeremy, Frankie Gallo (however this may not always happen), Jim Fitzgerald, Jimmy Pegorino, Dimitri Rascalov, Playboy X (however, his death is optional), Timur and Ray Bulgarin. Although Johnny Klebitz survived the events of GTA IV and its episodes, he was killed five years later by Trevor Philips.
 * Heroin can be purchased and sold in Grand Theft Auto: Chinatown Wars.
 * Jezz Torrent revealed in his song "Power Ballad" that he shot heroin.