Teenage Mutant Ninja Turtles is an American computer animated television series that premiered on Nickelodeon on September 29, 2012. It is the third animated Teenage Mutant Ninja Turtles television series and is produced by Nickelodeon Animation Studio. On October 2, 2012 and February 26, 2013, Nickelodeon renewed the series for a second and third season, respectively. The second season premiered on October 12, 2013.
Ninjutsu master Hamato Yoshi (Splinter) is carrying his four pet turtles through the streets of New York City when he encounters members of an alien race called the Kraang. During an altercation with these aliens, Hamato and the turtles are exposed to an alien chemical called mutagen and they undergo major physical transformations. Hamato Yoshi becomes a humanoid rat and the turtles become anthropomorphic. Splinter retreats to the New York City sewers, where he raises the four turtles as his sons and imparts to them his knowledge of ninjutsu.
Now teenagers, the Turtles venture to the surface for the first time and learn that the Kraang are using the mutagen as part of their plan to take over New York City. The Turtles befriend the teenage April O'Neil after she and her scientist father Kirby are abducted by the Kraang. Donatello develops a crush for April.
While Kirby remains a prisoner of the Kraang, April becomes an ally of the Turtles, who help her to find out where the Kraang have taken her father. April is also being trained by Splinter to be a kunoichi or female ninja.
The Turtles discover that the Kraang (who are under the leadership of Kraang Prime) have come to Earth from Dimension X and are plotting to use the mutagen to convert the Earth into a planet that will be suitable for their race.
The Turtles must now find and get rid of all of the remaining Kraang technology including mutagen before other people and animals get hold of it and are mutated by the Kraang. During this time, the Turtles gain new allies to help them in their mission and new enemies that antagonize them. However, Splinter and the Turtles are still struggling with their battle against the Shredder who is now an ally of Kraang Prime and the rest of the Kraang.