Here's everything you need to know about Lost.

Oceanic 815 leaves Sydney for Los Angeles and crashes on an island in the South Pacific. A very mysterious island. There are 48 survivors but some die later on. Jack is a doctor. He has a compulsive urge to fix things. Kate's on the run from the law for killing her dad. Sawyer is a conman. Locke is a cripple, but after the crash he can walk. Hurley won millions in the lottery but thinks it's a curse. Charlie is a heroin addict and a musician in a one-hit wonder band. He has acrush on Claire, the cute pregnant girl. Sayid was in the Republican guard and tortured people. Then there's Sun and Jin from Korea. They have marital issues. Michael and his son Walt are just getting to know each other. Walt is kind of special. After the crash, Jack helps everyone out. He becomes the defacto leader. Jack meets Kate. Kate stitches up Jack. They bond.
On the first night there's a monster in the jungle. There's other weird stuff too, like polar bears. Jack, Kate, and Charlie look for the cockpit. Kate learns Charlie was in the band Drive Shaft. They find the cockpit. They find the transceiver in the cockpit. The monster comes and eats the pilot. They get a signal on the transceiver. It's a French woman. speaking French. The message has been repeating on a loop for 16 years. Charlie asks "Where are we?" Locke kills wild boar; loves life on the island. Jin catches sea urchins. Claire's baby starts to kick. Jack starts seeing his dead father and it almost drives him crazy. Locke sees the monster. Sawyer hoards medical supplies. Shannon has asthma. Sayid tortures Sawyer for an inhaler. Sawyer just wants a kiss from Kate. They kiss. Sayid finds a wire on the beach. The wire lead to a trap. Sayid meets Rousseau, the French woman on the radio. Hurley conducts a census. He learns a guy named Ethan wasn't on the plane. Ethan kidnaps Claire. Charlie kills Ethan. Ethan was one of the Others.
The Others are the island's original inhabitants. They live in nice houses, have lots of food, hold book club meetings, and don't want to be bothered. They also can't have children. Women get pregnant and die. Locke finds a hatch in the ground. Locke tries many ways to open the hatch. Locke and Boone find a plane. Boone climbs up, it falls, Boone dies. Claire has her baby. She names him Aaron. Aah, the circle of life.
Michael builds a raft. His son Walt burns it. Michael builds another raft. Michael sets sail with Sawyer, Jin, and Walt. The Others come and take Walt. They blow up the raft. Locke blows open the hatch. There's a man down there. His name is Desmond. Desmond was in a sailing race and crashed his boat on the island. He pushes a button on a computer every 108 minutes, saving the world. The hatch is part of the Dharma Initiative - a scientific research project from the 1970s. They wanted to find out why the island is special. There's lots of food in the hatch. Desmond bolts and takes off on his boat. Locke starts pushing the button and thinks he's saving the world. Michael, Sawyer, and Jin wash ashore. They meet the survivors from the tail section of the plane: Ana Lucia, Libby, Bernard, and Mr. Eko. They make their way back to camp. Sun and Jin are happy to see each other. Sawyer gets sick. Kate is worried. Jack gets jealous. Kate sees a horse from her past. She freaks out. Jack consoles her. They kiss. Kate freaks out again. Jack is confused. Sun is pregnant, but Jin is sterile. What's up with that?
Michael iChats with Walt. Michael runs off to look for Walt. Michael gets caught by the Others. Sayid and Roussea catch a man in a net. He calls himself Henry Gale. He says he crashed in a hot air balloon. They think he's an Other, so Sayid tortures him. They lock Henry up. Henry plays mind games with Locke. Henry draws a map to his balloon, to prove he's telling the truth. But when they find the balloon, they also find the real Henry Gale, from Minnesota. So they know Henry is an Other. Henry tells Locke the button is a joke. Locke loses faith. The Others tell Michael that if he can free Henry, and bring back Jack, Kate, Sawyer, and Hurley, they'll give him Walt. Michael sets Henry free but makes it look like he was attacked. Meanwhile, the survivors see a boat coming to shore. It's Desmond. He's drunk. Locke tells Desmond the button is a joke, and they're going to see what happens when they don't push it. Michael, Jack, Kate, Sawyer, and Hurley set out to find Walt. Sayid, Sun, and Jin follow them with Desmond's boat. They see a statue with four toes. Very strange.
Sayid makes it to the Others' camp, but it's empty. Michael and the gang are ambushed by the Others, and taken to a dock. Henry gets off a boat. Hurley is told to go back to camp. He feels rejected. Henry takes Jack, Kate, and Sawyer prisoner, and gives Michael and Walt the boat to leave the island. Meanwhile, Locke and Desmond don't push the button in the hatch. The sky turns purple and the hatch is obliterated. The force from the explosion makes the island visible to the outside world for a moment. Two scientists in a snow hut someplace see a blip on a radar. They call Penny Widmore, Desmond's girlfriend, and tell her they found it.
Hurley finds Desmond running naked in the jungle. The hatch blew his clothes off, and now he can see the future. Jack, Kate, and Sawyer are taken to an abandoned Dharma station where they did experiments on polar bears. Kate and Sawyer are put in bear cages. Jack is kept inside and is greeted by Henry, who tells Jack his real name is Ben. Jack meets an Other named Juliet. Juliet brings Jack cheeseburgers. Juliet is a fertility specialist recruited by the Others to find out why all the pregnant women on the island are dying. Awhile back, Juliet told Ben he has cancer and needs surgery. Then Oceanic flight 815 crashed. Ben learned there was a doctor on board and now he wants Jack to fix him. Ben tells Jack he can go home if he does the surgery. Jack doesn't trust Ben and tells him to forget it. Kate tells Jack if he doesn't help Ben, "they're gonna kill Sawyer!" Kate and Sawyer think they're going to die, so they have sex. Jack sees Kate and Sawyer on an old TV. Jack says he'll do the surgery. Jack cuts Ben's kidney and says Ben will die if Kate and Sawyer don't go free. Jack tells Kate to never come back for him. Kate and Sawyer go free.
Jack and Juliet grow closer. Ben tells them they can go home. Kate, Locke, and Sayid come back for Jack. They see Jack play football with Mr. Friendly. Mr. Friendly throws like a girl. Kate gets caught by the Others. Jack tells Kate he's going home. Locke blows up the submarine that was Jack's ride. Jack is mad. Hurley finds an old Dharma van full of beer and a skeleton. The skeleton is Ben's dad. Ben killed him, and everyone else in the Dharma Initiative. Then he became the leader of the Others. Hurley gets the van started and takes a joyride with Charlie. Jack, Kate, and Juliet come back to camp. Locke says he's going to hang with the Others for awhile. They all think he's special.
The survivors don't trust Juliet; they think she's an Other. Jack says leave her alone. Desmond has a vision a woman parachutes on the island. Then, a woman parachutes on the island. Her name is Naomi. She has a picture of Penny and Desmond, and a phone. Naomi says she was sent by Penny and there's a rescue freighter 80 miles away. Naomi tells Hurley there were no survivors of Oceanic Flight 815. Juliet tells Sun that Jin is the father of her baby. Sun is happy. Ben is threatened by Locke. He takes Locke to see a guy named Jacob. Jacob lives in a creepy cabin surrounded by white ash. Ben talks to Jacob, but Locke can't see him. Locke hears Jacob say "help me" and all hell breaks loose. Now, Ben is really threatened by Locke. He takes him to a hole, where all the remains of the Dharma people are. Ben shoots Locke and leaves him for dead. Juliet tells everyone the Others are coming to take the pregnant women. Sayid tries to get a signal with Naomi's phone to call the freighter for help, but Ben is blocking all the signals to and from the island in an underwater station called the Looking Glass. It's connected to the wire Sayid found on the beach. Desmond has another vision of Charlie. In it, he flips a switch and drowns, but everyone else gets rescued. Charlie knows he's going to die so he says goodbye to Claire. Very sad.
Hurley wants to help Charlie, but he's too big. Charlie dives underwater and swims to the Looking Glass to flip the switch. The Others come for pregnant women. The survivors ambush the Others. Most of the Others get blown up, but Sayid, Jin, and Bernard get caught. Jack thinks Ben had them killed. Jack beats Ben to a pulp. Sawyer and Juliet try to help, but Hurley saves the day by running over the Others with the Dharma van. Jack leads everyone to the radio tower to make the call for help. Charlie flips the switch. Charlie talks to Penny on another old TV. She's never heard of Naomi. One of the Others, Patchy, blows up the Looking Glass. Water rushes in. Charlie writes on his hand: "Not Penny's Boat." Charlie drowns. Very sad.
Locke is ready to end it all in the Dharma grave. Walt appears. He tells Locke he's got work to do. Up by the radio tower, Naomi calls the freighter, but falls over with a knife in her back. Locke threw the knife; Jack is mad. Locke doesn't want to leave the island. Jack and Locke have a standoff. Jack calls the freighter anyway. The freighter says they will be there soon. Everyone is happy.
Flash forward to an unspecified time in the future. Jack is a broken man, living in L.A. Jack has a beard. He's a drunk and addicted to pills. Jack calls Kate on his cool new phone. They meet out by the airport. Jack tells Kate "we have to go baaack!"
So there you have it. Some will leave, some will not. Find out who in 2008.