In the year 2044, Leonardo runs through an active battlefield in a demolished New York. Casey and Leo are suddenly charged by Krang monsters, however, Michelangelo intercepts their attack. Leo declares the Earth's defeat by the Krang. He and Mikey then agree to send Casey back in time using a time gateway to prevent the Krang apocalypse from occurring by having him ensure the Krang remain in their prison dimension by retrieving and guarding its Mystic Key. Time reverse to 2020 before the apocalypse, Leonardo was leader of the Mad Dogs. On the Brooklyn Bridge, he bests Donatello's pizza box stack record and celebrates with him and Michelangelo before being alerted by Raphael of a theft unfolding by Hypno-Potamus and Warren Stone involving a strange key. The Turtles manage to stop them and they try to grab the key afterwards but the Foot Clan arrive and claim the Mystic Key and take off. April O'Neil trespasses into a laboratory and steals powerful herbicides. After doing so, April realizes she is being followed by a stranger as she leaves the building and would quickly knock him unconscious. April then notices a photograph of her, Splinter, and the Turtles. April takes the stranger to the lair where he wakes, overjoyed to see the family together. The family hasn't the slightest clue of his identity and the stranger explains that he is from the future, introducing himself as Casey Jones and would go on to explain that an alien species known as the Krang has invaded Earth in his future and need their help to stop the apocalypse!

Meanwhile, you were walking down the streets of New York, completely unaware of what was happening below the surface and the plans that was being unveiled.