THE DAY MARS INVADED EARTH

NASA successfully lands a robotic surveyor on Mars. The rover begins to explore, but after just a few minutes it is completely destroyed by what appears to be a high energy surge. At exactly the same instant back at mission control, Dr. Dave Fielding, in charge of the project, suddenly feels oddly disconnected and not himself; he shakes it off and then goes to face the crowd of expectant reporters. Right after he leaves, his exact body double is sitting at his desk.

Dave then leaves for a vacation and flies to California to be with his family; they are now staying in the guest house of a lavish mansion belonging to his wife's family. His children, 10 year-old Rocky and teen Judi, are very happy to see him, but it is very clear that his marriage to Claire is in trouble because of the time he must spend away from his family. At first, the tensions between Dave and Claire make it less obvious that they are seeing their body doubles walking around the estate. Eventually, though, as things turn strange, the whole family suspects something is wrong and pulls together. They soon discover they are trapped, unable to leave the isolated estate due to a malfunctioning main gate.

Dave then encounters his body double in the mansion's main house. The duplicate Dave informs him that Mars is inhabited and that all Martians are beings without any physical bodies, an energy-like intelligence. They traveled to Earth via the Martian probe's high-gain, two-way radio transmitter, destroying the robotic rover in the process. Now on Earth, the Martians plan to replace key humans with duplicates to quash any further Earth missions to Mars. Since Dave's wife and children would likely recognize a duplicate, they had to be replaced, too. Family friend Web comes by later and finally gets the main gate open, but on his way back, the Martian-Dave reduces Web to ash.

Later, "Dave and his family" appear to get into a car and leave the estate, with a Martian-Web duplicate behind the wheel. As they drive past the estate's empty swimming pool, five distinct body shapes of piled ash can be seen on the concrete bottom. The pool's water jets then turn on, slowly washing the ashes away.

The Fielding family is replaced by Martian duplicates and leaves the estate, while the real family's ashes remain at the bottom of the swimming pool.

The ending reveals that the Martian plot succeeds: the real Fieldings have been destroyed and replaced, suggesting the Martians’ covert invasion is underway. The image of ash in the pool, gradually washed away, underscores the erasure of the originals and the chilling efficiency of the Martian plan. It’s a bleak, understated finale that lingers, emphasizing the helplessness of the protagonists and the silent spread of the threat.