Leonardo (voice of JAMES ARNOLD TAYLOR), Raphael (voice of NOLAN NORTH), Donatello (voice of MITCHELL WHITFIELD), and Michelangelo (voice of MIKEY KELLEY) are four brothers -- teenage mutant ninja turtles -- who've gone underground after serving as crime fighters in New York City.
There's dissension among the ranks, however, since their sensei, Master Splinter (voice of MAKO), has sent Leonardo off to Central America for some sort of training, leaving Raphael bitter. Accordingly, while Donatello works as a tech-support phone operator and Michelangelo dresses up in costumes for children's parties, Raphael works as the Nightwatcher, a lone crime fighter.
He's occasionally joined by fellow vigilante, human Casey Jones (voice of CHRIS EVANS) who's seeing TV reporter April O'Neil (voice of SARAH MICHELLE GELLAR). She's been hired by wealthy businessman Max Winters (voice of PATRICK STEWART) to collect various ancient stone statues. Unbeknownst to her, Winters is a former general who once desired to rule the world, but his quest for power made him immortal, turned his soldiers into those stone statues, and unleashed thirteen monsters on the world.
With the work of April as well as ninja Karai (voice of ZHANG ZIYI) and her warriors, Winters is trying to reassemble his military team and capture all of those monsters. With the help of Master Splinter, the turtles eventually put their differences behind them so that they can battle both Winters' stone soldiers and those thirteen monsters.