S2·E16 The Dead Ringers

Batman and Robin escape Chandell's trap. Once back in the Batcave, they deduce his plan to get the Wayne family fortune by killing Bruce Wayne and Dick Grayson, then marrying the rightful heir, Aunt Harriet. In order to trap the villain, Bruce and Dick fake their own deaths. However, Harry has also figured out his brother Chandell's scheme, and desiring the Wayne fortune for himself, concocts a plan to masquerade as his twin brother.