The first season begins with a plane crash that strands the surviving passengers of Oceanic Airlines Flight 815 on what seems to be a deserted tropical island. Their survival is threatened throughout the season by a number of mysterious entities, including polar bears, an unseen creature that roams the jungle (the "Smoke Monster"), and the island's malevolent, and largely unseen, inhabitants known as "the Others". They encounter a French woman named Danielle Rousseau who was shipwrecked on the island 16 years prior to their crash. They also find a mysterious metal hatch buried in the ground. While two characters try to force their way into the hatch, four other survivors attempt to leave the island on a raft that they have constructed. Meanwhile, flashbacks centered on individual survivors detail their lives prior to the plane crash.
The second season follows the growing conflict between the survivors and the Others, and continues the theme of the clash between faith and science, while resolving old mysteries and posing new ones. A power struggle between Jack and John over control of the guns and medicine in the hatch develops, resolved in "The Long Con" by the machinations of Sawyer when he gains control of them. New characters are introduced, including the tail-section survivors (the "Tailies") and other island inhabitants. The hatch is revealed to be a research station built by the Dharma Initiative, a scientific research project that was conducting experiments on the island decades earlier. A man named Desmond Hume has been living in the hatch for 3 years, pushing a button every 108 minutes to prevent a catastrophic event from occurring. 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.
In the third season, the crash survivors learn more about the Others and their long history on the mysterious island. Desmond and one of the Others join the survivors, while one of their number in turn 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 aboard the freighter Kahana.
Season four focuses on the survivors dealing with the arrival of people from the freighter, who have been sent to the island not as part of a rescue operation, but for far more nefarious purposes. The reason specifically for the freighter folks being there is revealed. The survivors begin planning a way to get off the island before the freighter crew can carry out their plan. Flashforwards reveal the identities and future actions of the so-called "Oceanic Six," a group of survivors who have escaped the island and attempted to resume their normal lives. In an attempt to "move the island" to safety, one of the others uses an ancient device on the island that not only moves the island physically but also moves it to another point in time, while simultaneously teleporting that other to a desert in Tunisia.
The fifth season follows two timelines. The first takes place on the island where the survivors who were left behind 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 on the mainland after the Oceanic Six escape, and then follows their return to the island on Ajira Airways flight 316 in 2007 (three years after they escaped). Some passengers on the Ajira flight land in 1977 and some remain in 2007. The ones who land in 1977 reunite with the other survivors who have lived for three years with the Dharma Initiative. They then attempt to change past events in order to prevent their Oceanic plane from crashing in the future.
In the sixth & final season, the main storyline follows the survivors, reunited in the present day. Following the demise of Jacob, the island's protector, the survivors are up against the Man in Black, known previously as the Smoke Monster. A "flash-sideways" narrative also follows the lives of the main characters in a setting where Oceanic 815 never crashed. In the final episodes, a flashback to the distant past shows the origins of the island's power and of the conflict between Jacob and the Man in Black, who are revealed to be twin brothers. One survivor becomes the successor to Jacob as caretaker of the island, and kills the Man in Black in a final showdown, with the island at stake. A small handful of survivors escape on the Ajira plane. It is implied that a few survivors return home later, while others remain living happily on the island. The series finale reveals that the flash-sideways timeline is actually a form of limbo, where some of the survivors and other characters from the island are reunited after having died because their time on the island had been the most important part of their existence. In the end the survivors are all reunited in a church where they "move on" together.
