The survivors discovered the entrance to a mysterious building on the island. Under the leadership of Jack (Matthew Fox), they explored it. After forcing their way into the hatch, they found someone inside. It was Desmond (Henry Ian Cusick), whom Jack had met once in reality. As if seeing a savior, Desmond left a string of digital codes and ran away, and Jack and his party needed to take over his task - enter the code every 108 minutes to turn off the alarm. In the hatch, the survivors found enough food and learned about the background of the isolated island from a videotape, which seemed to be related to a failed experiment. On the other hand, Michael (Harold Perrineau) and others who tied up a bamboo raft and tried to leave the island did not successfully sail to the deep sea, but were taken to the other side of the island by the tide. They found a group of survivors at the tail of the plane, who held Michael and others hostage and slowly approached the camp...