This story takes place immediately after the events of TMNT Volume Two #9. After defeating the Baxter Stockman Robot, and unknown to his brothers, Donatello takes the robot's remains and sequesters them in a secret room hidden in the sewers. Why would he choose to reactivate their old enemy and more importantly, what is this new robot prowling the sewers?
Flashback from TMNT Vol. 2: The Baxterbot is demolished.