After a shipwreck Pi survives 227 days on a lifeboat with Richard Parker on board, a tiger. At first there were other animals as well, a hyena, a zebra with a broken leg, and an orangutan. The hyena kills the zebra and the orangutan, Richard Parker kills the hyena. Pi tells the story of how he survived, how he kept RP in check, what he ate, how he got the food, how he got water, and so on. Those descriptions are really disgusting at some times, especially the food and eating (I'm not sure if I wanna watch the movie). The way he tells the story in pretty convincing, there are al lot of impressions, feelings, and descriptions (well, apart from the flesh eating island).
In the end he ends up in Mexico, Richard Parker disappears into the jungle, and gets interviewed by people who want to find out why the ship sank. He tells them his story but they don't belive him, so he tells them another story without animals. The zebra turns into a sailor, the hyena into a cook, the orangutan into his mother, and Richard Parker turns into Pi. The cook first cuts of the sailor's leg (for bait and for food), then kills him (and eats parts of him), then kills Pi's mother, and Pi kills the cook (and eats his heart and liver).
It is never said what story is the real one. I want the story with the animals to be true because the other story is just too brutal. I mean, I know that people are capable of such things as cannibalism and stuff but I'd rather believe that you can survive with a tiger on board for 7 months than people killing and eating each other.