It's The Time Machine (1960) all over again. Post Apocalyptic times created a passive and ignorant human race called Eloi being raised for food by the monstrous underground-dwelling creatures called Morlocks. The Eloi are given free food and have no tasks or work to do. The sit around and eat the food given to them and each night when the siren tone is heard, dutifully line up and enter the caverns to be served up for the monster's dinner.