The Madmen Of Mandoras (1963)

Starring Walter Stocker, Audrey Caire, Carlos Rivas, John Holland, Marshall Reed
Directed by David Bradley
(actor & director credits courtesy IMDB.com)

Enemy agents kidnap a professor who's invented an antidote to a deadly gas, and take him to a foreign nation where one of history's greatest villains may still be alive. 

The main point of interest in this movie is the identity of the supposed man behind the plot, which I won't reveal here, but will say the film was later re-released with added scenes and a new title that gave his identity away.  The scenes without that villain and the sci-fi premise behind his preservation are pretty routine, and a largely unknown cast and an uninspired screenplay don't help matters.  It was good to see familiar 1950s character actors Rivas and Nestor Paiva, and the premise is a good one, but would have made a much better movie in more skilled hands.  It's still worth checking out if you've never seen it, but for me, it just wasn't a highly entertaining film.

Mysterious Island (1951)

Starring Richard Crane, Marshall Reed, Karen Randle, Ralph Hodges, Gene Roth
Directed by Spencer Bennet
(actor & director credits courtesy IMDB.com)

During the Civil War, a Northern captain and his friends escape the South by hijacking a hot air balloon, only to crash on a strange island where they face hostile natives and bloodthirsty pirates.

One of several adaptations of Jules Verne's novel continuing the adventures of Captain Nemo, this movie serial features a major departure from the text in the character of an alien invader from the planet Mercury, taking the place of some of the more fantastic elements of Verne's story.  Nevertheless, many sequences and characters from the book are preserved, although much of the adventure is replaced by standard fistfights and shootouts.  Still, fans of serials should be entertained, as I was, with Roth as always a fine villain, and Crane a noble hero.