A Certain Magical Index

Tōma Kamijō is struggling to complete his summer homework at home, but Index is just being a distraction to him. While Tōma takes Index to a restaurant for a change of location, they are attacked by a magician named Ōma Yamisaka, who kidnaps Index and runs off. As Tōma tries to find her, running into Mikoto Misaka along the way, Ōma prepares a ceremony that will allow him to access the grimoires inside Index's head in order to find a cure for a curse inflicted on a woman he has fallen in love with. As the ceremony begins, Ōma's body and mind is put through excruciating pain trying to access the grimoires. Thanks to Index discreetly using her new cellphone, Tōma is able to find her and stop the ceremony. Tōma gets Ōma to snap out his depression and offers to cure the woman's curse using his Imagine Breaker. Meanwhile, Motoharu Tsuchimikado witnesses Kaori Kanzaki fighting and defeating the Knights of England in Japan before parting ways.

Archbishop Laura Stuart informs Stiyl Magnus that The Book of the Law has been stolen and a skilled decoder named Orsola Aquinas has been kidnapped both by the Amakusa Catholics. She sends him, along with a group of Catholic battle nuns known as the Agnese Forces, to Japan to search for this grimoire as well as Orsola. In order to get Tōma's assistance, Stiyl pretends to kidnap Index. While Tōma coincidentally runs into Orsola on the way to save Index, the Amakusa Catholics appear and abduct her via a hole in the ground. After determining that the goal of the Amakusas Catholics is to use a special teleport magic to escape with Orsola before midnight, Tōma, Index, Stiyl and the Agnese Forces set up camp at the required location, where Tōma gets into a lot of awkward situations with the group's leader, Agnese Sanctis. Because Kaori was once an Amakusa Catholic, Stiyl knows he may have to fight her if necessary. Meanwhile, the Amakusa Catholics prepare to make their move.

The Agnese Forces face off against the Amakusa Catholics as a diversion while Tōma, Stiyl and Index sneak inside an amusement park. While escaping from some of the Amakusa Catholics, Tōma manages to find Orsola and gives her a crucifix necklace that Styil gave him earlier. The two are reunited with Stiyl and Index, who are facing against the leader of the Amakusa Catholics, Saiji Tatemiya. Working together, Tōma and Stiyl defeat Saiji and the rest of the Amakusa Catholics are captured by The Agnese Forces. However, the captured Saiji reveals to Tōma and Index that the Amakusa Catholics have never stolen The Book of the Law, as the real reason the Catholic Church wanted Orsola was to kill her to prevent the secrets of the grimoire from being abused. The Amakusa Catholics only got involved as Orsola sought them for protection but ran away as she did not trust them. Troubled by this revelation, Tōma asks Lucia and Angelene, two of the Catholic battle nuns, to see Orsola again but he accidentally angers Lucia, who tries to kill him, Index and Saiji. However, she and Angelene are forced to retreat when Index uses spell interception on Angelene's magic and counters Lucia''s attack.

Stiyl explains that the Amakusa Catholics will not kill Orsola until they can prove her to be a heretic. As Saiji leaves to free his comrades, Stiyl tells Tōma and Index to go home, since they have no further stake in this matter. Tōma, however, goes by himself to where Orsola is being held and tortured by Agnese, who reveals that her battle nuns deceived Necessarius to assist them. He is later joined by Stiyl, who reveals the crucifix necklace Tōma gave to Orsola means she is under protection of the Church of England, followed by Index and the Amakusa Catholics. While Tōma is put in charge in protecting Orsola, the others fend off the battle nuns, with Index utilizing Sheol Fear, the power to deafen and paralyze some of the battle nuns. However, Lucia brings another force of battle nuns, who willingly stab their ears to protect themselves from Sheol Fear.

As Tōma, Index, Stiyl, Saiji and Orsola barricade themselves from the battle nuns, Tōma and Index come up with an idea that Orsola could help them decipher The Book of the Law in Index's head to their advantage. When Orsola mentions her deciphering method, Index reveals her translations would be false, revealing Orsola was never able to really decode the grimoire all along. While the others fend off against the battle nuns, Tōma confronts Agnese, who attacks him with her Lotus Wand. However, Tōma manages to learn its attack patterns and lands a hit on Agnese. As Agnese tries to bluff that Tōma sacrificed his friends as decoys, they arrive with Innocentius, who Stiyl managed to summon thanks to the Amakusa Catholics. With her confidence broken, Agnese is knocked out by Tōma, breaking the battle nuns' morale, before Tōma himself falls unconscious. Waking up in the hospital in Academy City, Tōma is greeted and taken care by Kaori, who thanks him for helping and tells him that Orsola and the Amakusa Catholics are now under the protection of the Church of England. Meanwhile, back in London, Laura reveals to Stiyl that the true reason she got involved with the Orsola incident was to get the Amakusa Catholics under her control and use them as leverage to ensure Kaori's loyalty to Necessarius.

Kuroko Shirai goes out shopping with Mikoto, only to be interrupted her partner, Kazari Uiharu, who reports about robbers stealing an aerospace travel case. Kuroko subdues the thieves but is then attacked and wounded by their leader, another teleporter named Awaki Musujime. She reveals to Kuroko about Tree Diagram's destruction and how various factions are gathering of its remnants, the contents of the travel case being one of them. Kuroko manages to escape, but becomes concerned over what Awaki had told her, particularly concerning how Mikoto had been trying to stop them for reasons she had kept from her, namely being that if Tree Diagram were rebuilt, the Level 6 Shift experiment would start over again. As Mikoto goes out that night to confront Awaki, Kuroko decides to follow her and overhears their conversation before Awaki escapes. As Kuroko decides to take matters into her own hands, Misaka 10032 decides to take action.