It's no accident that Hermes is the name of the leader of the terror gang Mercury as Hermes is the Greek name for the Roman god Mercury. Allen Reisner, who plays Hermes, has almost 200 directorial credits to his name, including a dozen for Hawaii Five-O. This was his only acting credit.
In the pilot "Cocoon", Lew Ayres played the governor. Beginning with the third show, it was recast with Richard Denning for the remainder of the series, except when he appeared as U.S. Treasury agent Philip Grey in the sixth show "Twenty-Four Karat Kill".
Airing straight after The Finishing Touch (1973), this makes two episodes in row which hinge on the resident expert turning out to be crooked.
The signature "Mercury" on the ransom note looks the same as the nameplate on the front of Mcgarrett's Mercury car.