The walking dead roam the earth, used as vessels by invisible aliens intent on conquering humans. The terror begins when a famous physicist (John Carradine) is blown to smithereens in a nuclear experiment gone bad. His sudden death and the damage to the surrounding area and atmosphere leads Carradine’s good friend and colleague (Philip Tonge) to crusade for a limit to these experiments. He resigns and on the night of Carradine’s funeral, is visited by an alien in Carradine’s body. The thing has come to issue an ultimatum to citizens of Earth: surrender within 24 hours or face invasion and extermination.
Tonge tries to convey this message to his daughter (Jean Byron) her uptight scientist friend (Robert Hutton) and Washington officials, but you can predict their reactions. The poor man is mocked on the front pages of papers nationwide (in a very funny bit) and his warnings fall on deaf ears so the aliens issue their own, throw the planet into a panic and start their devastating attack. Suddenly Tonge doesn’t sound so cuckoo, so they make him the head of a new task force and lock him, Byron and Hutton in a bunker with the protection of a brave Major (John Agar). Tonge works on finding a way to beat the aliens, Byron and Agar work on making eyes at each other, and Hutton works on trying to contain his fear. In the space of a few days, the world burns and humanity is brought to its knees while these four test a chemical spray and an acrylic bath, and face failure until Hutton’s epic panic attack gives Tonge the brilliant idea he needs.
Invisible creatures and zombies are budget-friendly enemies. The aliens briefly appear at Carradine’s funeral as a pair of pale scaly legs, and then at the end as ghostly lizard-shaped humanoids (wearing the costume from It! The Terror from Beyond Space). At all other times you know they’re near when the geiger counter crackles, when the leaves rustle, or when unseen shuffling feet make tracks in the dirt (apparently this highly evolved species doesn’t lift their feet when they walk). They use human bodies to knock out hockey commentators and grab their mic to issue threats, or as armies of walking dead marching across the countryside searching for the bunker, and then all you need is a bunch of extras with black makeup smeared around the eyes. In any form, they sound like John Carradine. Nothing fancy in the effects department but just fine for this story, and nearly a decade before Night of the Living Dead.
So why do the aliens invade now? They’ve lived inside the moon for eons, paying little attention to us “slow” humans, but our development of spacecraft and nukes have convinced them to take over. Not that they’re peace-loving, mind you. Whatever moral there is here comes not from a wiser race of alien wagging its finger at our dangerous scientific ambition, but from the ability of mankind to pull together against a common enemy. Plus a bonus moral, that one hysterical wimpy male having a meltdown can help save the world.
There are ticking clocks, new deadlines and countdowns every few scenes: invasion starts at 11:30, there’s not enough time to spray them completely, or “we only have a few hours of air left in this bunker!” There’s a sound wave gun that needs to be aimed directly at the aliens, and bunker occupants can monitor outside activities with a closed circuit TV system that provides multiple angles and cinematic close-ups. Agar puts on a radiation suit that looks like it’s made out of terry towel, and vanquished aliens dissolve into mounds of suds. Director Edward L. Cahn did this in a short time, in few sets and locations and with spare effects, but it’s good alien-zombie fun.