Obviously, spoilers abound beyond this point. But if you're planning on watching the finale, you're probably not too worried about finding out what came before. Also, this isn't meant to be an all-encompassing summary of the series - just enough so that you can watch the finale without being any more confused than the rest of the "Lost" fans.
- Oceanic 815 crashes on an island while traveling from Sydney to Los Angeles.
- The major survivors are: spinal surgeon Dr. Jack Shepherd; fugitive Kate Austen; unlucky lottery-winner Hugo "Hurley" Reyes; con-man James "Sawyer" Ford; married Korean couple Jin and Sun Kwon; pregnant Claire Littleton; Iraqi torturer Sayid Jarrah; wise Rose Henderson; wheelchair-bound John Locke; Boone Carlyle and his spoiled stepsister Shannon Rutherford; heroin-addicted rock star Charlie Pace; construction worker Michael Dawson and his son, Walt.
- The island has supernatural properties. Locke regains his ability to walk, the survivors find and kill a polar bear and the Oceanic pilot is devoured by what looks like a black cloud of smoke (which fans quickly dubbed "the smoke monster").
- Also on the island are the "Others," a group with unclear intentions who are living on the island.
- While hunting for boar, Locke comes upon a piece of metal buried in the ground. He enlists the help of Boone to dig it out, and they discover it's the door to an underground hatch. There are numbers written on the door - 4, 8, 15, 16, 23, 42 - that are also revealed to be the numbers Hurley previously used to win the lottery. They show up often throughout the seasons, both on and off the island.
- Claire gives birth to a baby boy, named Aaron.
- Locke and Boone also discover a beech plane lodged in the trees in the forest. Locke instructs Boone to climb up to the plane, which crashes to the ground. He dies back at the camp.
- In hopes of leaving the island, Michael constructs a raft and sets sail with Walt, Sawyer and Jin. Another boat appears in the distance, but its captain and crew are members of the Others. They kidnap Walt and set the raft on fire.
- After Boone's death, Locke returns to the hatch and screams in anguish. A light shines up from inside the hatch, cementing in Locke's mind that it is his purpose to be on this island, and to open the hatch. Under fear of an attack from the Others, some of the survivors procure dynamite from the Black Rock, an old slave ship that crashed on the island centuries earlier, and blow the hatch door open.
- The hatch is revealed to be constructed by a scientific research team called the Dharma Initiative, that lived on the island in the 1970s. There are multiple stations throughout the island, with different names and purposes. The hatch is called the Swan, and is used to control the high amounts of electromagnetic energy around the station.
- Desmond Hume, a Scottish man who ended up on the island after his boat crashed there (he had been trying to sail around the world in order to impress Charles Widmore, the father of his girlfriend, Penelope), has been living in the Swan station, where he must press a button on a computer inside the Swan every 108 minutes. If he doesn't push the button, he claims, the world will end.
- Michael, Jin and Sawyer survive the raft explosion and wash up on the island shore, but are found by survivors from the tail end of the Oceanic 815 plane, which crashed on a different part of the island. This group is led by Ana Lucia Cortez, a Los Angeles cop with an extreme attitude. There is also Mr. Eko, a former Nigerian drug warlord, Libby, a wealthy widow, and Bernard Henderson, Rose's husband.
- Jin, Sawyer and Michael bring the Tailies back to the main camp, but en route Ana Lucia accidentally shoots and kills Shannon.
- A man named Henry Gale sparks a debate among the survivors - he claims his balloon crash-landed on the island (yes, that's Gale as in Dorothy and "The Wizard of Oz"), but some think he's a covert member of the Others. They lock him in the Swan's weapons room, and Jack and Locke argue over how to deal with him.
- Michael runs off into the jungle to find his son, and comes across the Others. They offer to give back Walt if Michael returns to camp and frees Henry Gale. He also must return to the Others with four people from the survivors camp: Jack, Kate, Sawyer and Hurley. Michael returns and carries out his plan, shooting and killing Ana Lucia and Libby in the process.
- Henry Gale, whose real name is Benjamin Linus, gives Michael a boat and instructs him and Walt to leave the island. Jack, Kate and Sawyer are taken as prisoners and Hurley is released with instructions to go back to camp and tell everyone not to come looking for their friends.
- Locke has a crisis of faith over whether or not pushing the button is truly necessary. Desmond reveals that he is the reason that Oceanic 815 crashed on the island - he pushed the button too late and the subsequent burst of electromagnetic energy caused the plane crash. Locke is not deterred and destroys the computer, but Desmond sneaks away to deploy the hatch's failsafe key. A piercing sound and flash of white light surround the entire island, and the Swan implodes and is destroyed. Everyone who was inside is safe.
- Scientists working for Desmond's love, Penelope Widmore, see the electromagnetic activity and locate the island.