There has been a rash of murders lately being attributed to someone who calls himself, the Mysterious Mr. M. The man responsible for the murders is actually Anthony Waldron (Edmund MacDonald). Waldron was believed to have been killed in Africa years ago. He returned in secret from Africa. With him he brought a drug called Hypnotrene. The drug is part truth serum and part mind control drug. Waldron plans on stealing the blueprints for a new type of submarine. He uses the drug on the inventor of the sub, Dr. Kittridge (John Hamilton). Not knowing the proper dosage, the drug also kills Kittridge by taxing his heart.
Assigned to find the mysterious Mr. M is Government Agent Grant Farrell (Dennis Moore). For assistance he calls on Police Chief Dan Blair (Joseph Crehan), Detective Kirby Walsh (Richard Martin) and Shirley Clinton (Pamela Blake), an insurance investigator.
For security reasons Kittridge had distributed the various parts of the sub construction to different vendors. None of them know what they are working on and none of them have the entire blueprint. Grant’s brother Jim Farrell (William Ching) owns one of the companies that is working on the submarine. Waldron kidnaps him and tries to use him as one of his minions to get rid of both himself and his brother. Grant manages to stop Jim but ends up injured.
Waldron is the nephew of Cornelia Waldron (Virginia Brissac). He is in league with Derek Lamont (Danny Morton) and his sister, Mariana Lamont (Jane Randolph). The Lamonts are companions to Cornelia. They keep an eye out on what is happening and advise Waldron. Waldron uses the Hypnotrene on anyone he feels has information or can help him complete his plans.
Waldron, Derek and Mariana soon hear from a man who says he has taken over the Mr. M alias. He then blackmails the conspirators to make them do his bidding. He tells Waldron to follow his instructions, or he will notify the police that he is still alive and what he is up to.
“The Mysterious Mr. M” was released in 1946 and was directed by Lewis D. Collins and Vernon Keays. It is a thirteen-chapter serial from Universal Studios. It is the 137th and last serial that Universal did.
During the opening credits of each chapter there are silhouettes and shadows of different people shown. The footage is from various other mystery films done in the forties. For example, one of them is Rondo Hatton from the film “The Brute Man” 1946. Others are from various Sherlock Holmes movies that featured Basil Rathbone and Nigel Bruce.
The beginning of each chapter has a couple minutes of recap on what happened in the previous chapter. Then they run the previous cliff hanger and show how the hero got out of it. Then there is a minute or two of recap on the entire serial, so far. It’s all pretty redundant if you’re watching more than one chapter at a time, but necessary if you’re a kid going back to the theater week after week. And week after week the bad guys and the good guys run around looking for whatever shiny object is needed to advance the serial to the next chapter. It is standard in its presentation, somewhat talky, but still fun to watch with a fair amount of action and some nice cliffhangers.
Chapter titles are... 1. When Clocks Chime Death, 2. Danger Downward, 3. Flood of Flames, 4. The Double Trap, 5. Highway Execution, 6. Heavier than Water, 7. Strange Collision, 8. When Friend Kills Friend, 9. Parachute Peril, 10. The Human Time-bomb, 11. The Key to Murder, 12. High-line Smash-up, 13. The Real Mr. M