Author and amateur astronomer John Putnam (Richard Carlson) and schoolteacher Ellen Fields (Barbara Rush) watch a large meteorite crash near the small town of Sand Rock, Arizona. They awaken a neighbor, who has a helicopter, and all three fly to the crash site. Putnam climbs down into the crater and notices a partially buried round object in the crater's pit. He comes to the realization, after he sees a six-sided hatchway close, that this isn't a meteorite but a large alien spaceship. The hatchway's noise starts a landslide that completely buries the craft. Putnam's story is later scoffed at by Sand Rock's sheriff (Charles Drake) and the local news media.
Even Ellen Fields is unsure about what to believe but still agrees to assist Putnam in his investigation. Over the next several days, local people disappear; a few return, but they act distant or appear somewhat dazed. Convinced by these and other odd events, Sheriff Warren comes to believe Putnam's story that the meteorite is actually a crashed spaceship with alien inhabitants; he then organizes a posse to hunt down the invaders at their crash site. Putnam, however, hopes to reach a peaceful solution to the looming crisis. Alone, he enters a nearby abandoned mine, which he hopes will eventually connect to the now buried spaceship and its alien occupants.
Putnam finally discovers the spaceship and learns from its crew that they crashed on Earth by accident; the aliens appear benign and only plan to stay on Earth just long enough to repair their damaged craft and then continue on their voyage. The aliens' real appearance, when finally revealed to Putnam, is entirely non-human: they are large, single-eyed, jelly fish-like beings that seem to glide across the ground, leaving a glistening trail that soon vanishes. They are also able to shape shift into human form using a telepathy screen in order to appear human and move around, unobserved, in order to collect their much needed repair materials. To do this, they copy the human forms of the local townspeople they've secretly kidnapped to help them repair their crippled spacecraft. In doing so, however, they fail to reproduce the townspeople's exact personalities, leading to suspicion and eventually to the deaths of two of the aliens.
To protect the aliens from the sheriff and his advancing posse, Putnam manages to seal off the mine in order to protect the aliens and to give them the time they still need to finish their repairs; they finally do so and leave Earth but not before releasing, unharmed, all of the missing townspeople who "assisted" them.
The aliens look like what sea creature?
jelly fish