Soul of a Heretic

Gedō no Tamashī (外道の魂) is the 1st chapter of the 15th volume and the 59th chapter overall of the Attack on Titan manga, written and illustrated by Hajime Isayama.

Overview
Nile Dok ponders over whether the Military Police First Interior Squad will use the new 3D Maneuver Gear against regular Military Police while the press attempt to get answers. Armin comes to terms with committing his first crime, although Mikasa, Levi and Jean encourage and thank him, respectively. Two soldiers, Hitch and Marlo, are caught when they stray from their patrol group and are detained by Squad Levi. Hitch learns about what happened to Annie after the battle at the Stohess District, while Marlo pleads to help Levi. Jean is given custody of the captured pair; he tests Marlo's honesty by having a brief fight, and Hitch tries to intervene. They both agree to aid the Survey Corps. Using Marlo's intel, the group locates what is very likely the First Interior Squad HQ where Eren and Historia are being kept.

Summary
The chapter begins with Roy and Beaure investigating the aftermath of the battle between the Survey Corps and the First Interior Squad. Beaure notes that the First Interior Squad is a separate branch from the regular Military Police, but is stopped by Roy, who apologizes to Nile Dok for Beaure's inexperience and tells him that the newspaper won't report anything on the First Interior Squad. Nile requests him to not report anything on the Anti-Personnel Three Dimensional Maneuver Gear either. He then proceeds to leave, wondering if the First Interior Squad will one day use such equipment against him as well.

The scene changes to a traumatized and crying Armin kneeling beside a tree, who vomits on the grass. Mikasa comes out of the stable and hurriedly goes over to comfort him; Armin asks Mikasa if she had experienced such psychological trauma as well, but then starts apologizing to her. Mikasa heads back into the stable, where Levi is shown getting stitches from Sasha on the shoulder wound he received from the First Interior Squad's attack. She goes over to Jean and tells him that it's his turn for guard duty, offering her rifle. A flashback of Armin saving Jean's life by shooting one of the Military Policeman on the carriage is shown.

A few hours later, the Special Operations Squad is sitting together, eating food beside a fire. Levi notices Armin's discomfort and asks him if he can't stand eating in a filthy stable, which he denies. It is revealed that Armin was the one to take the first shot despite Jean's attacker having drawn and point her gun first. The attacker's hesitation to kill Jean saved his life. Levi comforts Armin by explaining that had Armin not fired, Jean would not have survived the operation.

Hitch Dreyse, being ordered to accompany Marlo Freudenberg in an attempt to capture wanted Survey Corps members, is seen strolling deep into a forest alongside him. Hitch expresses her opinions on the recent events that happened in the Stohess District, and questions where Annie is, also telling Marlo that she was her roommate when Annie served in the Military Police. Their conversation gets interrupted when Hitch hears the sound of water and silences Marlo, asking him to get his gun ready. The two see Armin Arlert getting water from the nearby river.

Hitch and Marlo both order Armin to put his hands up into the air, only to fall into his trap. Mikasa and Levi then jump behind the two. Mikasa and Levi then proceed to take their guns away from them and rid of their other weapons and uniforms. Levi questions Hitch and Marlo about their current positions in the Military Police. Hitch, angry at the Survey Corps, blames Levi and the entire military branch for the aftermath of Stohess and of Annie's death. Hitch and Marlo soon learn that Annie was the Female Titan that was in Stohess and she is captured and still alive. Marlo tells Levi that he would like to help the Survey Corps, but Levi doesn't buy in and orders Sasha to escort them someplace else. Jean interferes and offers to take the two instead. Taking Marlo and Hitch to the area, Jean threatens them with a knife along the way.

Arriving at the spot where Jean wanted them to be at, Jean admits he intends to kill the two of them with the knife he had believing them to be a threat and cannot be trusted. As Marlo explains that Levi didn't want Jean to kill them, Jean says that this was his own personal decision, and that none of the other members don't know about it. Jean raises the knife in the air as the two beg for their lives to be spared about to stab them to death, but Jean trips and the knife falls from his hands. Marlo grabs the knife and tells Hitch to run. Jean and Marlo are soon struggling for the knife when Jean gets back up on his feet. Jean tells Marlo that he also has a gun that can hurt them, and that it would be of more use as it shoots faster than how a knife can stab. Marlo confesses that he really was on their side, and his personal view of the Military Police Brigade. They both stop struggling when Hitch grabs a nearby stick and rams it into Jean's head, sending him to the ground. Hitch attempts to hit him again with the stick, but is stopped by Marlo. Marlo tells Hitch that Jean was only testing him, and he never was serious on killing them after all. Marlo questions Jean about why he trusts him so much, and Jean responds by saying that Marlo reminds him of someone he hated, by that he was referring to Eren, and calls Marlo a blockhead. Marlo reaches his hand out to help Jean up, and Jean confirms that Marlo and Hitch can be trusted and their strength could be of use.

Hitch and Marlo lead Mikasa, Connie, Sasha, Levi, and Jean to the Interior Brigade Compound, where they are ready with rifles. Levi says that it was thanks to Hitch, Marlo, and Jean that they made it this far. They all continue their way to the Compound, saying it is their time to strike.