Contains spoilers for this episode and earlier episodes.
Desmond abruptly runs from a meeting and dives into the sea, rescuing Claire before the others realize she is drowning. Hurley believes he can see the future, and Charlie joins him in trying to obtain an explanation. They get Desmond drunk, but their questioning becomes confrontational. When Charlie calls him a coward, Desmond attacks him. The episode then follows Desmond's experience after turning the hatch's failsafe key, when he finds himself back in London with Penny.
Desmond recognizes fragments of his island life while apparently reliving the past. Charles Widmore rejects his request to marry Penny, and Charlie appears as a street musician who does not recognize him. Desmond tries to prove his foreknowledge to a physicist friend, but his predictions initially fail. A ring-shop proprietor, Ms. Hawking, describes the future he remembers and argues that events correct themselves when someone tries to change them. Desmond nevertheless struggles against repeating his decisions.
He breaks up with Penny after they pose for their familiar photograph. Later, the pub events he had predicted occur on a different night, and intervening leaves him struck by a bat. He wakes naked on the island beside the hatch's remains. Back in the present, Desmond explains that his lightning rod and his rescue of Claire were attempts to save Charlie from deaths he had foreseen. He fears further intervention cannot prevent Charlie dying, leaving Charlie shaken by the prediction.