小大卫麦克林有一个问题——镇上所有的成年人在看到奇怪的灯光在他家附近的一座小山后不久就开始做出奇怪的行为。随着越来越多的成年人受到影响,他必须向漂亮的布莱克医生寻求保护。最终,他必须以一个不同寻常的结论来面对自己的恐惧。One night, young David McLean sees a spaceship crash into a nearby sandpit. His father goes to investigate, but comes back changed. Where once he was cheerful and affectionate, he's now sullen and snarlingly rude. Others fall into the sandpit and begin acting like him: cold, ill-tempered and conspiratorial. David knows that aliens are taking over the bodies of humans, but he'll soon discover there have been far more of these terrible thefts than he could have imagined. The young doom-monger finds some serious help in a lady doctor and a brilliant astronomer. Soon they meet the aliens: green creatures with insect-like eyes. These beings prove to be slaves to their leader: a large, silent head with ceaselessly shifting eyes and two tentacles on either side, each of which branches off into three smaller tentacles. It's up to the redoubtable earth trio to stop its evil plans.