ABC World News Tonight With David Muir

A sudden plane crash leaves survivors stranded on a jungle island.

Jack tends to a wounded man who reveals a secret about Kate.

Jack and Hurley discover an alarming secret about Kate, as the marshal's life hangs in the balance and he suffers a lot of pain. In flashbacks, we see Kate when she was arrested by the marshal in Australia.

A shocking secret about Locke is revealed.

A pregnant Claire's health takes a bad turn from lack of fluids.

Walt and the others are shocked when Michael is brutally beaten, but only the non-English-speaking Jin and Sun know the truth behind the attack. In flashbacks, we get a glimpse of Jin and Sun's married life prior to the crash.

Survivors struggle to free Jack when he's buried alive in a cave collapse. In flashbacks, we see Charlie as rock star drawn into a world of drug abuse.

Shannon's inhaler runs out and Boone believes Sawyer has the remaining three in his stash. In flashbacks, we hear Sawyer's story and find he is not who he says he is.

Sayid's life is placed in grave danger after he stumbles upon the source of the mysterious French transmission, the woman Danielle Rousseau. In flashbacks we meet Sayid's childhood friend Nadia.

Claire has a horribly realistic nightmare about her new baby being harmed or kidnapped. In flashbacks, her life with the father of the baby is revealed.

Boone and Locke discover another island mystery. In flashbacks, we learn more about Jack's relationship with his father.

A rising tide threatens to engulf the entire beach encampment.

Kate is puzzled by the revelation that Sun can speak English.

Sayid enlists Shannon to help decipher the French woman's map.

Ethan threatens to kill other survivors unless Claire is returned to him. In flashbacks, Charlie charms a woman and attempts to get clean.

Kate and Sawyer divulge dark secrets to each other while tracking a renegade boar that Sawyer swears is purposely harassing him. In flashbacks, a shocking connection between Sawyer and Jack is revealed.

When the raft the survivors have been building mysteriously burns down, Michael is convinced that Jin is responsible for the sabotage. In flashbacks, more details of Jin and Sun's troubled marriage are revealed.

Hurley flashes back to the experience he had before boarding the plane.

Locke thinks he's being sent a sign on how to get the hatch open.

Jack tends to a severely wounded Boone after Locke returns him to the caves while Claire unexpectedly goes into labor while deep in the forest. In flashbacks, we see how Jack met his wife.

Sayid engages Locke to uncover the truth about Boone's death. In flashbacks, we see the events that landed Sayid on the plane and how his faith and loyalty were put to the test.

A secret from Kate's past is revealed to the other survivors on the island.

Jin, Michael, Sawyer and Walt ready the raft for sailing. In flashbacks, we see the survivors' final moments before they boarded the plane.

The castaways on the raft run into unexpected trouble. Meanwhile, the remaining islanders attempt to blow open the hatch. Flashbacks continue to show the survivors' final moments before boarding their fateful flight.

A visitor to the encampment could be a threat to Claire's infant son.