A plane crash strands the surviving passengers of Oceanic Flight 815 on a seemingly deserted tropical island, forcing the group of strangers to work together to stay alive. Their survival is threatened by mysterious entities including polar bears, an unseen creature that roams the jungle, and the island's hostile inhabitants known as the "Others". They encounter a Frenchwoman named Danielle Rousseau who was shipwrecked on the island over 16 years earlier and find a mysterious metal hatch buried in the ground. An attempt is made to leave the island on a raft.

Most of the story, which continues 45 days after the crash, focuses on the growing conflict between the survivors and the Others, with the continued theme of the clash between faith and science being important in certain episodes. While some mysteries are resolved, new questions are raised. New characters are introduced, including the tail-section survivors and other island inhabitants. More island mythologies and insights into the survivors' pasts are divulged. The hatch is explored and the existence of the DHARMA Initiative and its benefactor, the Hanso Foundation, are revealed. As the truth about the mysterious Others begins to unfold, one of the crash survivors betrays the other castaways, and the cause of the plane crash is revealed.

The story continues 67 days after the crash. New crash survivors and Others are introduced, as the crash survivors learn about the Others and their history on the mysterious island. One of the Others and a new island inhabitant join the survivors while a survivor defects to the Others. A war between the Others and the survivors comes to a head, and the survivors make contact with a rescue team.

The season focuses on the survivors dealing with the arrival of people from the freighter Kahana, which has come to the Island, and the escape of the Oceanic Six (their post-island deeds being shown in flashforwards).

Season five follows two time lines. The first takes place on the island where the remaining survivors erratically jump forward and backward through time until they are finally stranded with the Dharma Initiative in 1974. The second continues the original timeline which takes place both off the island and following the Oceanic Six's return to the island on Ajira Airways Flight 316 in 2007.

(Information Source: Wikipedia - http://en.wikipedia.org/wiki/Lost_(TV_series))