I’m going to bumume that whoever read this isn’t clueless and is up to date with Lost, so don’t blame me if I spoil anything.

Oceanic Six get off island

Island starts skipping through time, causes deaths

Locke leaves island, causes skips to stop, people still on island are stuck in 1977

Locke convinces Oceanic Six to return

Ben kills Locke

They get on a flight thats going over the island, all but Sun and Ben are transported to 1977, Locke comes back to life

Two timelines take place now: 1977: All the survivors are living with the Dharma Initiative, 2008: Sun, Ben and the other crash survivors including Locke meet up with the natives. (Richard and co.)

1977: They theorise they can cancel out every event up to this point and continue their lives as normal if they detonate a hydrogen bomb to stop the Swan from every being built, which caused the plane to crash originally.

They succeed in detonating the bomb, but we have yet to see the result.

2008: Locke takes everyone to see Jacob, guided by Richard.

Ben kills Jacob under Locke’s orders, Locke is revealed to be a nemesis of Jacob from long ago.

That’s pretty much it. There’ll be bits I missed out, but those are the major plotpoints of Seaon 5. Screwed up, TELL ME ABOUT IT.