Episode 20 of "Lost"
s01e20 Do No Harm

Jack tends to a very wounded Boone after Locke returns him back to the caves after his body was nearly crushed in the plane fall when trying to contact the outside world. Sun helps Jack in his need for medical assistance and Sayid presents Shannon with a grand romantic surprise when they're alone. Claire unexpectedly goes into labor in the forest while a helpless Kate, Charlie and Jin go into panic mode by her side when Jack is unable to deliver the baby and they must tend to Claire themselves. Meanwhile, Locke mysteriously goes missing during all the chaos when returning Boone back to Jack. He disappears back into the forest.