After encountering mutants and ninjas, Casey Jones decides to take on "pure evil" alone. When he meets Raphael, the two hot-headed fighters must put their dislike for each other aside and work together against a common foe.
Facing Shredder's deadly new assassin, Leo must decide whether to risk his brother's lives or ask for Splinter's help. Donnie must put aside his rivalry with Casey in order to uncover a new Kraang plot.
When Raph accidentally damages a Kraang machine, it allows him to switch brains with a Kraang. Now he must find a way to convince his brothers and Splinter that it's really him, before the Kraang controlling his body destroys his brothers or worse, reveals their location to the rest of the Kraang.