In East City, Colonel Roy Mustang discusses his recent reassignment to Central City over a game of chess with his own mentor, Lt. General Grumman. As a parting gift and to celebrate Roy's first victory, Grumman gives his protege the chess set and allows him to transfer Lt. Riza Hawkeye, 2nd Lt. Jean Havoc, 2nd Lt. Heymans Breda, Warrant Officer Vato Falman and Master Sgt. Kain Fuery to the capital with him. Outside the city in the Ishvalan slum, Scar trains his injured body back to his former strength and is visited by his old mentor, who softly reprimands his pupil for embarking on the path of blood and hatred. He advises Scar to break the chain of hatred, but before the words can sink in, a pair of bounty hunters arrive to claim the price on the Ishvalan murderer's head, having been informed of his whereabouts by Yoki, an Amestrian beggar living in the slum due to the Elric brothers' destruction of his military career. Understanding that his presence has attracted unwanted attention for his countrymen, Scar quickly dispatches the two bounty hunters and departs from the slum despite his mentor's assertion that Scar's brother would be grieved by the path he has chosen.

Back in Dublith, Alphonse receives a secret message stating that there are people who know his secret and requesting that he meet them nearby -- alone. Al complies and encounters Dolcetto, Roa and Martel, who wish to take the Elric boy to see their mysterious boss. Unfortunately for them, Alphonse is unwilling to accompany them any further and begins a short skirmish. Martel, displaying her inhuman agility, invades Al's body and dampens his movements long enough for the behemoth Roa to subdue him physically and as Alphonse struggles, the boss arrives on the scene and explains that the strange foursome are all chimeras who work under him. Al is bound and transported to the gang's secret lair, where the boss introduces himself as Greed. Alphonse challenges Greed's earlier declaration, stating that chimeras advanced enough to pass as human are an impossibility, but Greed retorts that the concept of "impossible" is, itself, an impossibility and explains that Martel, Roa and Dolcetto were humans alchemically spliced with the genes of a snake, ox and dog, respectively, while many other members of their gang were combined with a host of other creatures by the military. Subsequently, Greed explains that he, too, is not human. Displaying an Ouroboros mark on his left hand, he declares himself to be a homunculus - an artificially created person. Alphonse retains his skepticism, but to prove his existence, Greed orders Roa to knock off his head with a sledgehammer and, right before Al's eyes, Greed's head grows back in a matter of seconds as if the damage had never been done. Getting down to business, Greed interrogates Alphonse on his existence as a soul bound to a non-living object, citing that the Elric boy's state is the closest thing to immortality - Greed's own ultimate goal, for though he is roughly two centuries old and monstrously resilient, he is not truly immortal. He demands to know the secret of Al's body, threatening to take him apart for analysis if he doesn't comply, but Al remarks that his brother was the one who performed the procedure.

Edward, looking for his missing brother, is instead met by the lizardman, Bido, who has been sent by Greed to gather information regarding Alphonse's soul binding. Unfortunately, Bido is no match for Ed, who beats him up and gleans Al's location from him. Angrily storming into Greed's stronghold, Edward learns that the man is a Homunculus and, seeing the Ouroboros tattoo, asks why Greed doesn't simply consult his comrades Lust and Envy. Greed explains that he is no longer in contact with them and instead proposes a trade - he will tell Edward how to create an artificial human body for his brother in exchange for the information on soul binding. Edward furiously rejects Greed's offer and instead makes threats of his own, turning the discussion into a fight. After Ed dispatches Dolcetto, Greed orders Roa to take Alphonse away for analysis while he takes care of the Fullmetal Alchemist. Edward tries intercede, but is held at bay when Greed displays yet another ability and coats his hands with a mysteriously impenetrable film of armor. Unable to injure his new foe, Edward asks what Greed is made of, to which the Homunculus replies that, while he has inhuman regenerative powers and what he calls his "Ultimate Shield", his body's composition is similar to that of a human's. Greed reprimands Edward's folly at losing his temper and starting a fight instead of making a deal and gaining the information he wants, but Edward steadfastly refuses to comply and posits that all he has to do to win is target the parts of Greed's body not covered by armor. However, Greed merely laughs as he allows the strange armor to coat his entire body, revealing his true form.

Izumi and Sig, discovering the Elrics' disappearance, are informed that they were each seen entering a local bar called the Devil's Nest. Meanwhile, Edward finds himself on the losing side of the fight against Greed, with his automail arm badly damaged. But having had time to think about his predicament, he finds a loophole in Greed's strategy. Reasoning that, with a body composition roughly equivalent to that of a human's, the only substance that can be forming Greed's Ultimate Shield armor must be carbon, which makes up a third of the human body and whose molecular structure determines whether its consistency resembles that of a diamond or mere graphite. With that in mind, Ed transmutes the structure of the armor, making it flimsy enough to allow for several damaging blows on his opponent's exposed flesh. And learning from this that Greed cannot produce the armor and regenerate his wounds simultaneously, Ed suddenly gains the upper hand despite being too injured to keep the fight up for much longer. Just then, however, Izumi bursts onto the scene and - having overheard their conversation from outside, begins her own assault on the Homunculus.