Okay, I can try. It’s been a while since I watched that episode.
So pretty much it’s a big Desmond episode. There’s flashbacks that show him being released from a military prison, and that he’s a big Charles Dickens fan. It also reveals that he got his boat from Libby and that when he sort of washed up on the island he met a man named Kelvin. Kelvin was the dude who pushed the button before Desmond and he was secretly sneaking off everyday to try to fix Desmond’s boat. Desmond figures this out one day and flips out and accidentally kills Kelvin and that’s also when he was away from the hatch too long and the electromagnetic field started going berserk which caused 815 to crash.
During the “current time” parts of the episode Desmond comes back to the island and is totally hammered. Jin, Sun and Sayid take Desmond’s boat around the island to try to sneak up on the others to rescue Walt. Of course that doesn’t work out as planed. Michael lures Jack, Kate, Sawyer and Hurley off into the jungle but Jack already knows about Michael’s plan to give them to the others. Locke and Desmond have an argument in the Hatch about the button. Locke smashes the computer. Desmond freaks out and when things in the Hatch start to shake he digs out the “fail safe” key and when he turns it in it’s special little key hole the Hatch blows up.
Ben (aka Henry Gale at this point) sends Michael off on a boat with Walt. He also sends Hurley back to the beach but keeps Jack, Kate and Sawyer under his control. At the end it shows Penny Widmore receiving a phone call about an electromagnetic anomaly.
I think that’s close to everything.