Some TMNT stuff really isn't for little kids.
Slash has taken out Donatello and Raphael and is about to do the same to Leonardo but Michelangelo is able to stop him. All the Turtles rally against him but Slash is as aggressive as ever, and the fight goes on.
On Burnow Island, Baxter Stockman is on a video-call with Chet Allen back at StockGen. Stockman expresses his extreme displeasure about Slash's escape to Chet, but concedes that if the creature can at least hunt down and kill the Turtles, it will have done what it was meant to. Stockman tells Chet he will be occupied with General Krang's project for a while and won't be back for some time. Elsewhere on Burnow Island, Krang gives a speech to his troops, informing them of the impending full-scale assault their enemy in Smada City.
Back at April's parents' antique shop, the others worry that the Turtles aren't back yet. April decides to go and look for them and says she'll drop Casey off at his ice hockey game on the way, but Casey wants to help her search instead. Splinter decides to wait there in case they return while April and Casey are gone.
In the church's bunker the Turtles continue fighting Slash. Donatello tells his brothers that Slash was psychologically programmed to hunt down and kill them, and will continue to try to do so until he's dead, meaning they have to kill him. Raphael agrees with Donatello, but Michelangelo and Leonardo want to try and end things peacefully if they can. Leonardo attempts to put Slash in a sleeper hold while the others wear him down. They appear to be near victory when Slash throws them all off, his stamina nowhere near out. Slash tells them to keep it coming. Slash begins to attack again but Leonardo hits him with a shuriken and tells him it has to stop. Outside, April and Casey arrive and enter the church. Inside, Leonardo attempts to talk Slash out of hunting them, to no avail. Slash lunges at Leonardo, who, distracted by April and Casey's arrival, accidentally stabs Slash in the neck with one of his swords. Slash is seemingly mortally injured, and falls into the sewer.
The next day, everyone is helping clean the dirty bunker to make it more suitable to live in. Michelangelo has gone to pick up some pizza and Leonardo meditates downstairs. When Michelangelo arrives at the pizza shop, he finds a note from Woody, saying their friendship has to end due to the baggage that Mikey brings, deeply upsetting him. Downstairs, Leonardo sits staring at the sewer where Slash fell in, preoccupied with guilt from killing him.
In the epilogue, Slash has washed up on the shore and is awoken by Old Hob. Hob tells him about all the traits they share, and how together they can strike back at Stockman and everyone else at StockGen.