The Magnetic Monster is a truly novel science fiction film, in terms of its cerebral plot and low-key, quietly intense execution. As much a mystery film and a manhunt as a sci-fi-thriller, it pushed lots of suspense buttons for viewers in 1953 and still holds up a half century later. Richard Carlson (who also co-produced) plays Dr. Jeff Stewart, an agent for the Office of Scientific Investigation. Stewart and his colleague, Dr. Dan Forbes (King Donovan), are called in when unusually strong radioactivity is detected in the Los Angeles area -- this ties up with a seemingly inexplicable case of super-magnetism at an office building. Soon they are on the trail of a rogue research scientist, Dr. Howard Denker (Leonard Mudie), who, working on his own, has created a new element called serranium, which is not only highly radioactive, but dangerously unstable. Every few hours, the serranium mass grows, adding to itself by absorbing the energy from the atomic structure of any matter around it, releasing massive amounts of radiation in the process. This phenomenon manifests itself, in part, as the super-magnetism that they've witnessed, and is accompanied -- at the moment of the growth cycle's conclusion at that phase -- by dangerous implosions, collapsing the structural integrity of whatever surroundings it happens to be in. As the serranium mass grows, its energy needs also increase, along with the intensity of the magnetism and the implosions. The danger lies not only in the immediate destructive power of the serranium's rapidly increasing energy absorbtion, but its increasing mass, which, at some point, will threaten to unbalance the Earth itself, in its rotation and orbit. Long before that, however, the radiation is going to start killing large numbers of people, and the destructive force surrounding it will threaten the integrity of the Earth's surface, much as an extremely powerful thermo-nuclear weapon might. Denker is dying of radiation poisoning when they find him, and Stewart and Forbes are left to work out a way out of the danger he has left behind with his discovery. They recognize that the only hope they have of stopping the process is to get ahead of it, by bombarding the serranium with energy from the most powerful cyclotron in the world, more than it can contain in its present mass, which should -- so they calculate -- cause it to split into two stable elements. The last section of the film is a race against time, to cut through official red tape and get it safely to the accelerator (in Canada) before the next absorbtion cycle begins; if they miss the deadline, not only will it destroy anyone and anything in its immediate vicinity, but there won't be enough power on the face of the Earth to prevent the next cycle, which will threaten the whole world.
~ Bruce Eder, All Movie Guide