Kate's original crime that started her life on the run is revealed. Meanwhile, the survivors lay one of their own to rest, Kate sleeplessly watches over a feverish Sawyer, and Mr. Eko has a surprise for Locke regarding the hatch.
When Charlie's vividly surreal dreams lead him to believe Claire's baby, Aaron, is in danger, Locke suspects Charlie may be using drugs again. More of Charlie's background story shows his difficult relationship with his heroin addicted brother. Meanwhile, Sawyer encourages Hurley to act on his attraction to Libby.
Survivors fear that "The Others" may have returned when Sun is injured during a failed kidnapping attempt. Meanwhile, Sawyer is an amused, but highly interested, bystander when tension escalates between Jack, Locke, Kate and Ana Lucia over control of the hatch computer, and the storage of the weapons.
The mysterious French woman, Danielle Rousseau returns to lead Sayid to a mysterious captive who claims he crashed on the island. Meanwhile, Sawyer recruits Hurley to help him find another island animal that is harassing him: a loud tree frog.
When Claire's baby falls ill, she becomes determined to find out what happened to her to regain her memory during her captivity with the Others, triggering flashbacks to her experience among the Others, and her ordeals concerning her baby. Also, Mr. Eko learns about Henry Gale and asks Jack and Locke to give him a meeting with their captive.
When Sun comes to the realization that she might be pregnant, she struggles on whether to tell Jin about the situation. After no success from Jack or Sayid, Ana Lucia is called in by Locke to interrogate the prisoner, Henry Gale, to get more information out of him about how he arrived on the island. Ana Lucia, Sayid, and Charlie then set out into the jungle to try and confirm Henry's story.
When the hatch suddenly takes on a life of its own, Locke is trapped alone in the bunker and is forced to enlist the help of an unlikely ally: the captive Henry Gale to try to free him. Meanwhile, Jack faces off against Sawyer in a series of card games for supplies. Also, Ana Lucia, Sayid and Charlie find out the truth about Henry in the jungle.
Hurley begins to think the island is affecting him in a very strange way, so Libby attempts to offer him support. Hurley also recalls his past in a mental hospital with his friend Dave. Meanwhile, the prisoner calling himself Henry Gale offers new information about the Hatch, which severely shakes Locke's sense of purpose.
Jack and Kate bring an exhausted Michael back to camp where he has news about "The Others". Meanwhile, Ana Lucia attempts to get the prisoner, Henry Gale to confess to being a spy for the Others, and he attempts to kill her. Also, Hurley plans a surprise date for Libby.
Mr. Eko enlists Locke to help find a secret location he believes houses answers to the island's mysteries. Meanwhile, Jack, Sawyer, and Kate struggle to cope with the horrific situation in the hatch following the escape of "Other" Henry Gale, and of the shooting deaths of Ana-Lucia and Libby, unaware that it was Michael who is responsible.
Michael's whereabouts during his 13 days in captivity in the "Others" camp are detailed while in the present, he tries to convince Jack to help him mount a search party for his son Walt still being held captive. Meanwhile, Locke struggles with a choice whether or not to abandon the hatch.
After discovering a sailboat just offshore containing former hatch oversee Desmond, Jack and Sayid come up with a plan to confront "The Others" and hopefully get Walt back. Meanwhile, Eko and Locke come to blows as Locke makes a potentially cataclysmic decision regarding the "button" and the hatch.