Injured in a fall, the President of the United States is in desperate need of surgery -- and the operation must be kept secret. Naturally, Seaview is chosen as the best place for the operation. An enemy agent, taking the place of the doctor who would have used a radiological device on the President, will attempt to kill the Commander-in-Chief with a deadly ray. Will she be discovered in time to save the President?

Admiral Nelson is aboard a new submarine when it is destroyed by a giant jellyfish. Nelson and the first officer are the only survivors. The two men begin a desperate battle for survival while being presumed lost at sea by the navy.