When the heroes are briefly captives of the villains, Dr. Mabouse turns from the Hornet to his driver/bodyguard/enforcer and says, "And this can only be Kato." A few minutes (running time) later, as the now freed masked men race in the Black Beauty to catch up with Mabouse's truck, the Hornet addresses his assistant as Kato with a captured Mabouse henchman sitting right next to him. This is the only episode of the series (although it also happens during the "Batman" crossover) in which the error of applying the name Kato publicly to the costumed identity ("the Hornet's man" as he was anonymously referenced, usually) rather than have it restricted to the civilian one (Reid's valet), is made. The distinction was also consistently held to on the original radio series and the two Saturday matinee serials. The slip here is probably the result of the writer and the director, as well as the man who got the "Produced by..." credit, of this two-parter having not otherwise worked on the program and not knowing any better, with the regular cast not really caring.
Mike Axford is credited but doesn't appear.
There is some question as to whether or not this is actually the final episode, as several sources list the showing of "The Hornet and the Firefly" the following week as its premiere, rather than a rerun from 30 December 1966.