The Foot have invaded the sewers searching for the Turtles, who in turn have taken refuge at April's apartment. Leo, sickened by the injustice and helplessness of it all, vents his anger in an early morning exercise run which soon turns into a fight for survival. If this episode seems familiar to you, it's because the story line has been adapted from one of the early issues of the original comic book run (Leonardo #1), and a similar scene was also depicted in the 1990 Ninja Turtles live-action movie (with Raphael in place of Leonardo). The setup is simple; place Leonardo in ever-escalating brawls contrasted against cutaway moments with the rest of the family goofing around at home, blissfully unaware of the danger about to come. There's good use of the various divisions of Foot Ninja here, from the low-level grunts (who become increasingly easier to take out as the series progresses) to the invisible Foot-Tech, Hun, and finally the Elite Guard. These guys are serious scene-stealers, and deservedly so. The show once again raises the bar for action intensity, and we get a good gauge on 4Kids censorship policies here - no blood is allowed, but multiple bruise patches effectively convey how seriously beaten the characters become. Like the original comic, there is little dialogue in the Leonardo scenes and the episode is visually dark and moody.
An exceptional effort that leads into the climactic arc of season 1.