A comet crash lands in rural Iowa and the government investigates. They find an obviously fake, man-made UFO structure and the locals giving tours of this "alien ship". But this is really where the manta ray-like aliens landed and where they started taking over people. They latch onto their spines and control them. The main focus is on agents Sam Nivens (Eric Thal) and Mary Sefton (Julie Warner). Their feelings for one another are tested when he's first taken over, then saved, and when she's possessed and tries to deceive him. The aliens have moved into the city and have created this big, hive-like structure--and it's up to these agents to stop them from taking over the world.
This is an interesting adaptation of the Robert Heinlein novel, though it seems much more inspired by the '79 version of INVASION OF THE BODY SNATCHERS. In fact, it stars Donald Sutherland (who starred in that movie) and the puppeteered individuals also do that weird round mouth thing, like they are silently screaming. Throw in Will Patton (FALLEN SKIES) as a creepy scientist who admires the aliens, and other actors who have been in alien movies-- Yaphet Kotto (ALIEN) and Keith David (THEY ALIVE). Still, it's a decent alien invasion movie and an okay version of the Robert Heinlein novel.