As Charlie lets this realization sink in, Desmond is hurrying back to the signal room when he notices that Mikhail is gone. Desmond starts running towards Charlie, but Charlie has already figured out that Mikhail is not where he is supposed to be since Mikhail is outside the station, tapping on the window. With a grenade. Charlie realizes what is about to happen, but instead of running out of the room and slamming the door behind him, he stays in the room, locks himself in, and stands there while Mikhail detonates the grenade, shattering the window, and quickly filling the room with water. Instead of just writing chucklehead, chucklehead, chucklehead, I'm going to assume that Charlie was too panicked to think straight and opted to sacrifice himself to save Desmond. It seems sweeter, sadder, and less idiotic that way. As the room fills with water, Desmond pounds on the window with a fire extinguisher trying to break the glass. Charlie manages to keep his wits about him enough to write on his hand (with a Sharpie, of course!) the incredibly important fact that it is "Not Penny's Boat." He slams his hand against the window and Desmond gets the message. Desmond tears up as Charlie makes sure he understands. He floats away from the window and crosses himself as he crosses over to the great unknown. On land, Aaron cries as Charlie dies. Claire tries to comfort him, but when Naomi asks what's wrong, Claire says that Aaron is just scared. Naomi says she doesn't blame him. Just then her phone chirps and she pulls it out to read that the Channel is Open. She asks Claire, "What's your boyfriend's name?" Claire looks confused so Naomi clarifies, "The rock star who swam down to the station?" Claire is all, "Oh that boyfriend! Charlie. Why?" Naomi answers, "Because he just got us rescued." So Charlie's great sacrifice was worth it. I'm sure Desmond will sleep easier knowing that.