A group of people, living in an underground cave, are forced to sit with their backs to the entrance; all they can see is the far wall of the cave. In the mouth of the cave is a large fire, and between the fire and the peoples back parade various creatures, whose shadows are cast by the fire on to the cave wall. The prisoners in the cave cannot turn their heads to see the creatures; all they can see are the flickering shadows on the wall in front of them. Since this is all they have seen since the day they were born, they think these shadows are all there are.
In Plato's story, one of the prisoners manages to free himself and, looking around, realizes that everything he took to be reality is but a shadow. Outside he finds the true world of color and three-dimensional forms. Overjoyed with his discovery, he returns to his former companions to tell them the good news. But try as he may, he cannot convince them that everything they see are but flickering shadows of the "real world". In the end the other prisoners kill him rather than accept such a nonsensical notion.