A group of scientists and sailors land on an island to finish the work of a previous group which vanished without a trace. Strange sounds are heard, tremors are felt, and pits open up in the ground leading to a series of caves. As members of the party go missing, their voices can be heard luring the others to them. The voices turn out to be coming from giant crabs which have absorbed the personalities, memories, and possibly even the souls of the people they're eaten. In an attempt to gain the rest of the humans, the crabs have been tunneling through the island in order to make vast sections of it collapse into the sea, leaving the stranded humans with less and less area to retreat to.
I haven't seen Attack of the Crab Monsters (1957) since I was a kid. The plot actually doesn't seem too bad, but this is really a thirty minute movie with forty minutes of padding; people hiking, people scuba diving, people running, people talking about things that don't really move the plot forward and pseudoscientific notions that are unnecessary and bring everything to a standstill. There are also far too many characters in this movie, almost all of whom are superfluous to the plot. There's a really cool not-quite animated opening titles bit which for some reason shows a giant octopus destroying some sunken wreckage rather than a crab. I think the crabs themselves are kind of neat looking, though my eleven year old son complained that their legs didn't move when they did and compared the entire movie to The Giant Claw (1957). (My wife and daughter left the room shortly after the movie started). The crabs were more convincing than Pamela Duncan's eyebrows which looked like they were drawn on with a Sharpie.
I'd like to say that I really enjoyed it, but I didn't. It was entertaining in parts, but there was far too much dead space between those moments.