In the tower near the safehouse, Hawkeye struggles with Gluttony, who seems wholly unaffected by her merciless gunfire. Just as the voracious monster prepares to devour her whole, however, Black Hayate and Fuery intervene, distracting Gluttony long enough to free Riza and commence a second barrage of bullets. Still, Gluttony refuses to be subdued until Roy bursts onto the scene and blasts the creature out of the tower with a fiery explosion, expressing relief that he made it in time to help. Hawkeye, however, is less than pleased and scolds Mustang for revealing himself to the enemy. Discovering that Barry's human body is on the move, Mustang and Hawkeye get to ground level, secure a car and pick up Havoc in order to follow, but suddenly run into Alphonse, who has come to help. While Barry chases his body, the four in the car follow his trail. Hawkeye wonders aloud if Gluttony is really dead, citing that he continued his attack despite having been shot in his vital areas multiple times and Alphonse declares that her enemy must have been a Homunculus. Mustang declares that such a being cannot exist, but changes his tune when Al reveals his encounter with Greed and explains that these creatures have remarkable regenerative properties. As Roy begins to lament having to deal with such inhuman monsters, Gluttony rises once again, his injuries gone.

Barry's trail stops at Central Alchemical Laboratory #3, where Roy declares that the lab's very involvement already implicates members of Military Command in the ongoing conspiracy and orders a retreat as they already have what they need. The Chopper, however, has other plans and storms into the facility after his body. Quickly crafting a new plan to take advantage of the situation, Colonel Mustang orders everyone else into the building and announces to the laboratory staff that he is chasing a fugitive that has just entered. Mustang, Havoc, Hawkeye and Alphonse follow Barry's path to an underground level of the facility and split into two groups to search - Jean with Roy in one pair and Riza with Al in the other. No sooner do Havoc and Mustang discover an abandoned experiment chamber, however, than they are greeted by Lust, who mockingly scolds Jean for betraying her. They notice her Ouroboros tattoo and mark her as the enemy, prompting Roy to ask her if she had anything to do with Hughes' death. When she states that she did not deliver the finishing blow, but was involved, Roy shoots her in the leg and demands that she get on her knees for interrogation. But when her wound heals before their eyes and she states that it will take more than that to get her on her knees, the two soldiers realize that the woman before them is a Homunculus. Amused at how much they know, Lust uses her bladed fingernails to pry open her chest cavity and reveal the Philosopher's Stone that acts as her core - fueling her regeneration and other powers with its energy. Realizing that she has only shown them this because she does not intend to let them survive, Roy initiates an attack, but when Lust splits an overhead water pipe with her claws, drenching Roy and effectively crippling his Flame Alchemy, he and Jean are forced to flee the room. Thinking quickly, Roy uses the Transmutation Circle on his glove to deconstruct the water filling the chamber into combustible hydrogen and flammable oxygen and - taking his cue - Jean tosses his cigarette lighter inside, causing an explosion which engulfs the Homunculus in flame.

Jean and Roy reenter the room to investigate but just as Roy warns his comrade to be on the lookout for Lust's regenerative powers, her fingers burst from the rubble, impaling Havoc through the abdomen. Roy attempts frantically to stir the fallen and exsanguinating 2nd Lt. as Lust rises from the ash, her body rapidly reforming. Taking up Havoc's carbine, Roy shoots a hole in her chest and rips out her Philosopher's Stone, declaring that he will use it to heal Havoc's wounds. Without her core, Lust crumbles to dust, but before the Colonel can make it to Jean's side, the Homunculus' body quickly and grotesquely reforms around the Stone in his hand before her claws pierce his stomach as well. Lust shreds Roy's Flame Alchemy glove and leaves both men to die while lamenting that such a valuable Human Sacrifice had to be lost. As she walks off after the others, Roy orders Havoc not to die before him. Outside, Führer Bradley arrives on the scene and informs the soldiers at the gate that he will be entering the building alone to offer support to Colonel Mustang.

Riza and Al finally catch up to Barry in a huge white room with an enormous pair of stone doors only to find that the Chopper has finally mutilated his human body. Barry laments that his human form has decayed so profoundly and suggests that fastening a soul to an incompatible body is impossible. Hearing this, Al begins to wonder how long he has before his own soul rejects and comes apart from his metal container. Lust appears on the scene, expressing anger at Barry's betrayal of his masters and distress at Alphonse's presence - as it means she will have to slay two Human Sacrifices in one night. Barry throws him self forward to attack Lust, but is swiftly cut to ribbons by her fingers. Turning to the other two, Lust promises to send Riza to Mustang's side and the Lieutenant, piecing the Homunculus' words together, flies into a rage and opens fire with multiple sidearms before succumbing to grief and collapsing in tears over Roy. Lust moves in for the kill, but Alphonse steps in the way, defending Riza from attack. As Lust carves away at Al's armor body, Hawkeye pleads with the young alchemist to flee and leave her behind, but Alphonse refuses, stating that he will not allow any more of his friends to die.

Roy appears at the entrance and commends Alphonse for his statement and as the armor boy erects a stone barrier to protect himself and the lieutenant, the Colonel unleashes a torrent of flame upon Lust, finally bringing her to her knees. Shocked and scorched, Lust realizes that the Flame Alchemist is transmuting with the flint from Havoc's lighter and a Transmutation Circle carved into the back of his hand and has used fire to cauterize his wounds shut. As he fires wave after wave of hellfire upon her, Roy informs Lust that if it really does take more than a normal killshot to subdue her, then he will simply have to keep killing her until she stays dead. Ablaze and in agony, Lust charges, but her Philosopher's Stone runs out of energy before she can strike Mustang down, causing her and it to disintegrate to nothing. As she dies, she compliments the Colonel's focus and determination, but remarks that his straightforward eyes will soon grow cloudy with despair. Mustang collapses in exhaustion and thanks Al for protecting Riza before requesting that an ambulance be summoned for Havoc. In the entrance hall, Bradley watches the scene but quietly sheathes his sword and walks away.

Back at the hotel, Winry waits worriedly for Al on the front steps. He arrives moments later, looking quite the worse for wear and she greets him through relieved tears just before his right arm falls off completely. Meanwhile, in the large, white chamber, Barry's Blood Rune remains intact, rendering him still alive, but unable to move. His human body, on its last breaths, drags itself over to the rune and scratches it out, ending both their lives.

Edward returns to Resembool and bids Breda and Major Armstrong farewell before heading toward Pinako's house, but as he approaches, he sees a familiar figure standing before his mother's grave and comes face-to-face with Van Hohenheim.