In the hatch, an unconscious Charlie slowly wakes up among the rubble and the sparking wires. The sound is muffled with a little bit of ringing. I guess we're hearing through Charlie's ears. The question is, is this because of the blast or because of Driveshaft? He makes his way down the hall, yelling Eko's name, and finds him, lying unconscious and bloody under a beam, that Charlie moves, and yells at Eko to wake up.
Inside the computer room, there's less than four minutes left, and Desmond's saying they need to push the button, and Locke's arguing. "Do you not hear me, brother? I crashed your bloody plane!" he says, and fills Locke in on the flashback we just saw, and Desmond JUST REMEMBERED FOR THE FIRST TIME, apparently, and shows Locke the date of the system failure. "It's real! It's all bloody real! Now push the damn button!" he yells. Locke's still sticking to his Pearl station story. He believes in Pearl station as much as he used to believe in Swan station, apparently. Desmond decides that if Locke won't do it, he will, but Locke picks up the computer and smashes it on the floor. Desmond's absolutely horrified: "Now I'll never wrap Karateka!" He also (or maybe only) says, "You killed us. You killed us all." Locke says he just saved them all. The natural response would be for Desmond to say, "You killed us all, infinity," but Desmond just runs to the control panel and sparks the wires so the blast doors go back up, and when they do, he runs out of the computer room over to the bookcase. Charlie's still trying to revive Eko, and asks if Desmond can help him. "I'm trying, brother," says Desmond. But you're late for your book club? Desmond finds what he's looking for: his copy of Dickens' Our Mutual Friend.
We flash back to a despondent Desmond in the hatch, sitting at the table, with a gun, and a bottle of booze, which he's in the process of polishing off. He's also got Our Mutual Friend. Ready to read, ready to die. He opens it, and an envelope falls out, simply labeled :"Desmond." He opens it and unfolds the letter, which is one of those special talking letters that record the writer's voice so you can hear it as you read it. The letter's from Penelope, which she says she's writing as Desmond's leaving for prison, and she's hiding it in the one place he'll turn to in a "moment of great desperation." In prison? I don't imagine it would have been so easy for Desmond to read while bent over, so whatever, Penelope. She says she knows he's going away "with the weight of what happened" on his shoulders, and he's the only one who can take it off. "Please don't give up, Des. Because all we really need to survive is one person who truly loves us. And you have her. I will wait for you. Despite the many suitors who keep coming around. Always. I love you. Pen."