The City of Ember: Chapter 9

In chapter 9, the Door in the Roped Off Tunnel, Lina shows Doon the papers she found, and Don showed her the Roped off tunnel. But when they were there, they learned they weren't the first ones to find the door. While they were there, they heard footsteps, and grunts, so they hid. After the person unlocked the door and went into the room. Then the person ran out really fast. Lina and Doon thought the person was going to save the city. But Lina thought she had recognized him...

QUESTIONS: Who do you think the man (or woman) was? what do you think they were doing? Will that person save the city?