During an excursion above the sewers, Splinter is injected with a miniaturized device designed by Baxter Stockman. As his sensei grows weaker, Donatello investigates and discovers Splinter is being attacked from the inside by microscopic mousers! Initial attempts to combat this infection fail, so Donatello makes the only rational decision: to shrink himself and the other Turtles down and fight the micro-mousers head on! Can the Turtles save Splinter? Or will they all fall to the tiny invaders? Find out in the fourth exhilarating episode of Teenage Mutant Ninja Turtles: Saturday Morning Adventures, "Big Trouble in Master Splinter"!
