The Seaview is exploring an underwater area that is pretty volatile with seismic activity. After a shockwave hits and it is discovered that a layer of sediment is hiding the floor, divers are sent out to have a closer look. It is then realized that there is a city on the floor, along with many mysterious capsules scattered about. One is brought onto the Seaview, and many crew members (along with Harriman Nelson and Lee Crane) are trying to get it open. There appears to be no way to trigger an opening, nor will the most powerful blowtorches, acids, etc. make a dent in the capsule. A man is seen inside a small window, who awakens, then begins suffocating, then ceases moving after a while, appearing to have died.