The Daihasei Festival has commenced, meaning that the renowned all-girls' school, Tokiwadai Middle School, is also participating. Mikoto Misaka, the "Ace of Tokiwadai," is competing, but other participants are still putting in their best efforts despite her overwhelming strength. But, there's more than just games and entertainment. The festival opens Academy City to the outside, and various factions have begun plotting to infiltrate it. Misaka has become a target for some, and as the festival goes on, shadowy figures start to emerge. Toaru Kagaku no Railgun T brings back Tokiwadai's Ace and her friends, delving deeper into the darker side of Academy City. Terrorist attacks and wicked underground projects are what could potentially occur in this city.