|We're both getting the battle we've been waiting for. Let's put an end to this here. Humanity, or those damned Titans. One of us will survive...and the other will die.|
|— Erwin Smith prepares for a battle against the Titans|
Eren succeeds in sealing the hole in Wall Maria with his Titan powers, but it seems everything was too easy. Levi reminds him that their enemies can breach the Wall again at any time, so until they find and kill them, the mission is not over. Armin finds traces of a campsite and three empty mugs of some black liquid similar to tea nearby not long ago, and Erwin leaves him in charge of the Survey Corps to direct their search mission. Under Armin's orders, the Survey Corps search all over the district until Armin eventually leads them to search inside the Walls, thinking that it may be their most plausible hideout. Armin's hunch is correct and they find Reiner, who quickly kills the soldier who located the hollow spot within the Wall where he hid. Levi attacks and cuts Reiner's nape and chest, but fails to kill him and the latter transforms into the Armored Titan, though still laying on the ground and appearing to be fazed by his injuries. The Beast Titan then appears leading an army of Titans, and launches a rock aimed at the inner gate of Shiganshina, blocking the only entrance and trapping the Survey Corps inside the district without their horses. Planning to kill or be killed, Erwin and the corps ready themselves for an all out battle, as the Armored Titan rises and the Beast Titan and his army approach.
Eren reaches the hole in Wall Maria and transforms into Titan as the rest of the Survey Corps watches. Using his hardening ability, Eren seals the hole in the Wall before emerging from his Titan form, at which point he is retrieved by Mikasa and they return to the top of the Wall. Hange Zoë asks if the process worked, and two soldiers on the ground report from both sides of the Wall that the process worked. Mikasa begins to fret over Eren, and lends him her own cloak when he notes that his cloak burned away during the transformation.
Eren assures Hange that he is fine after using his hardening ability, and the rest of the Corps begins to head towards the inner gate of Shiganshina District to seal it too. As they leave, Eren expresses his disbelief that he has really closed the hole in Wall Maria, but is reminded by Levi that they are not done yet, as Bertolt and Reiner will simply destroy the Wall over and over again as long as they are left alive, and that the Corps' mission to retake Wall Maria will not be over until they have killed the two. Eren assures Levi that he has not forgotten this fact.
Elsewhere, Erwin and a soldier look on as the latter notes that Reiner and Bertolt are not attacking, and wonders if they are hiding because they can not handle the Corps' assault. Armin then arrives, informing them that he found a full set camping equipment abandoned at the base of the Wall. Armin tells them that Bertolt and Reiner had apparently been drinking something resembling tea, and that the pot they had been using had gone cold. He also shows them three cups he found containing traces of the liquid, noting that there were apparently more than just two people atop the Wall.
Erwin notes that at the rate the Corps was moving with their horses and vertical maneuvering equipment, there was no way that a freshly-used pot would have time to cool. Erwin deduces that Bertolt and Reiner must have had some way to know that the Corps was approaching at least five minutes in advance, which would give them plenty of time to prepare. Based on Erwin's observations, Armin realizes that there were possibly scouts in addition to the three atop the Wall, and that the Corps may be facing far more enemies than previously thought. In response to this revelation, Erwin informs Armin that finding any hidden enemies is now the Corps' top priority, and asks Armin to use his sharp mind to help the Corps in their new objective.
As he waves over a squad of soldiers, Erwin instructs Armin to take as many soldiers as he needs and search the area around the inner gate for any enemies. After being informed that they will be operating under Armin's command, the soldiers immediately inform Armin that they have completely searched the Wall, and ask where they should search next. Armin instructs them to split into two groups and search the surrounding buildings on both sides of the inner gate, and to let everyone know if they have found anything with acoustic shells.
As Armin and his squad depart, the soldier accompanying Erwin notes that Erwin took a big gamble by giving Armin a squad, but Erwin assures him that he made his decision based on Armin's accomplishments. The soldier informs Erwin that Eren's group is approaching, and asks if the operation should be put on hold while they search for any hidden enemies, but Erwin informs him that the operation will continue as the Corps cannot remain in enemy territory for long. Erwin notes that the Corps' only option is to fight a quick battle, as they cannot beat their enemies in an extended fight. As he speaks, Erwin solemnly notes that Reiner and Bertolt are not the only ones with something to hide.
As his squad searches, Armin desperately wonders what he should do, as his group has yet to find any of their enemies, even as Eren's group draws nearer. Armin wonders if Reiner and Bertolt did not attack before Eren sealed the hole because they intended to wait to attack until Eren was exhausted from using his ability, reasoning that if this were the case, they would be hiding nearby so that they could attack immediately. However, his squad has yet to locate them in any of the logical hiding places.
Armin begins to panic, noting that everything is riding on the operation, and that if they fail, everything will end. He notes that Erwin will not stop the operation, and that even if the enemy is given the perfect opening, the Corps will have no choice but to fight them. As he thinks, he notes that Bertolt and Reiner always find new and original ways to attack, and that the Corps is always left at a disadvantage because they know nothing about the Titans. As he thinks this, Armin remembers the Titan that was hidden inside Wall Sheena, and fires his flare gun, having come to a realization.
As his squad reconvenes atop the Wall, asking Armin if he found anything, Armin orders them to search the Wall. Bewildered, the soldiers protest that they already have, but Armin tells them that they must search the inside of the Wall, because there must be a space inside the Wall for humans to hide. The soldiers rebuff this idea when he admits that it is only a hunch, but Armin reasons that their enemies always use their Titan shifting abilities in improbable ways, claiming that the Corps will never gain the upper hand if they constrain their themselves to common sense.
Erwin interrupts shooting a flare to silence everyone present, which is seen by Eren's group, who wonder if the operation has been halted. Hange orders everyone to spread out atop the Wall. Erwin informs Armin's squad that there are times to be rigid and times to be flexible, and orders them to follow the chain of command. Armin instructs his squad to split into two groups and search the Wall again, this time carefully checking everything from the door up. The soldiers are unsure, but obey, and begin searching the Wall.
Eren's group is confused to see Armin's squad searching the sides of the Wall, and Connie and Jean question whether their squad should have stopped, while Eren wonders if Armin has discovered something. As Armin watches the soldiers search the Wall, he notes that Bertolt and Reiner needed a position where they could always respond to Eren approaching the Wall to seal it, and where they could keep a constant eye on the situation. He notes that if Bertolt and Reiner do not know that the Corps knows about the Titans inside the Walls, then they will not expect the Corps to search for them inside the Wall.
Suddenly, one of the soldiers finds Reiner hidden inside a hollow section of the Wall. The soldier fires a flare but Reiner emerges and stabs him, to everyone's horror. Armin is too shocked to move, even as Reiner begins to approach him, but Levi quickly attacks Reiner, slicing his nape and stabbing his chest. However, this does not kill Reiner, and Levi, alarmed, kicks him to the ground below, wondering if Reiner's survival is another "Titan power" he possesses. As Reiner shifts into his Titan form, Levi laments that he was not successful in killing him.
Witnessing Levi's fight with Reiner, Erwin begins to order the Corps to search their surroundings for any other enemies, but is interrupted by a loud sound behind him. Turning, Erwin is faced with the sight of dozens of newly-transformed Titans, led by the Beast Titan; who takes a rock and hurls it in the Corps' direction. The projectile hits the base of the Wall, causing the soldiers to assume he missed them, but Erwin notes that the Beast Titan used the rock to block the Corps' entrance to Shiganshina at the northern gate, leaving them trapped and without their horses. Erwin explains that their enemies are planning to wipe them out by cutting off their escape route. As the Titans approach, Erwin declares that the Corps is finally getting the fight they want, and that they will put an end to it here.