Raphael goes to the nearest Post Office, grabs a wanted poster, and makes up his face to appear as none other than Mad Dog McMutt and heads for the park. What Raphael does not know is that the real Mad Dog is taking a walk in the very same park and, after an encounter with a stray dog over a bone, is knocked unconscious and left hidden in the bushes.
The other three Ninja Turtles, who have been following Raphael, enter the park, find the McMutt wanted poster and realize that Raphael is disguised as the notorious criminal figure.
A few minutes later, the other three Turtles find the real McMutt who they believe to be Raphael -- only he has lost his memory and cannot remember who he is. The Turtles convince him that he is Raphael until he is attacked by the same stray dog, knocked down and regains his memory. McMutt pretends to be Raphael until he learns that the real Raphael is impersonating him and that his thugs believe that Raphael is McMutt.
Meanwhile, April and Irma have been caught by McMutt's thugs when they break into McMutt's hideout. Raphael reveals his true identity to them but his ruse is soon discovered when the real McMutt shows up.
April, Irma and Raphael are taken along for the ride when McMutt and his thugs "commit the crime of the century" which is literally stealing the Museum of Natural History -- it seems that McMutt has a thing for bones -- especially dinosaur bones.
His plans go awry when Irma and April get peeved enough to take on McMutt himself.