The members of the underworld organization ITEM finish one mission, and are called in to defend the remaining facilities. When Misaka tries to infiltrate one building, she encounters Item member Frenda. Meanwhile, Nunotaba drops in at the other facility.

As Misaka continues her way into the research facility, she and Mugino play a game of cat-and-mouse. Meanwhile, at the other facility, Nunotaba sneaks into a control room, planning to disrupt the experiment by adding a new factor to the Misaka Network.

Having realized who Misaka is, Mugino decides to give her a run for her third-place ranking. When Frenda mistakenly leaves her doll-bombs behind while heading to the other facility, Misaka collects them and uses them to supplement her diminished powers.

With the end of summer vacation approaching, the girls plan a study session at Saten's apartment to catch up on homework. Everyone is to bring an ingredient for a potluck stew party, but most have trouble deciding what to buy, leading to some surprises.

Edasaki is due to be discharged from the hospital, and it is learned that she will be living with Haru'ue. The move is bittersweet for Uiharu, who is losing her roommate, but she feels it is for the best. Meanwhile, a new movement is afoot in the city.

Therestina reluctantly provides Misaka with the clues she needs to find the group behind Febrie's secret. With Kongo's help, the girls identify Aritomi as the man they are pursuing, and find out more about him and his company, the STUDY Corporation.

Shirai, Konori, Kongo and friends, and Uiharu and Saten confront the powered suits at the four Assembly sites, where they soon receive backup. Misaka and Febrie move to take on Aritomi directly, but he has one final surprise up his sleeve for them.