I explained it to Fawkes, and copypasted it for you. I cut out all of Fawkes's "comments"...
Charlotte: Night fell, and Charlotte's infection took over her, and she frantically tried to leave.
Charlotte: The door was barred, so she went out Tim's bedroom window.
Charlotte: She left a hole, and the infected got in.
Charlotte: Everybody moved to the next apartment and blocked them off.
Charlotte: Sarah saved Jesse.
Charlotte: Then, the next day, Charlotte returned "mysteriously", nobody knew what had happened.
Charlotte: They decided to find a new place to live, they split up into two groups.
Charlotte: Mark and Tim went for supplies.
Charlotte: Sarah and Charlotte looked for a new house.
Charlotte: Went with the supply people.
Charlotte: Sarah had figured out that something was up with Charlotte and confronted her.
Charlotte: Charlotte finally revealed (to Sarah only) that she was, in fact, infected.
Charlotte: But she was different than the others because she could control herself most of the time and her skin wasn't nearly as sensitive.
Charlotte: Then, they found an insane asylum with already barred windows to stay.
Charlotte: Charlotte went in and cleared it of the infected, as they won't attack her.
Charlotte: Then, they headed to the place they were planning to meet the other group.
Charlotte: On the way, Charlotte revealed a little about her past.
Charlotte: She lived in London most of her life, moving to New York for an internship at the New Yorker.
Charlotte: She was on vacation with her fiancee when the infection took over.
Charlotte: They were attacked the first night of it and she became infected.
Charlotte: When she was first infected, she couldn't control herself, and ended up killing her fiancee.
Charlotte: Then, they got to the meeting place, and went inside because there was a juke box.
Charlotte: They were dancing, when suddenly, infected attacked, as it was dark in there
Charlotte: *.
Charlotte: Timothy got bitten, and Charlotte told them to leave, because she was having difficulty controlling herself.
Charlotte: It was because Tim was bleeding all over the place.
Charlotte: They left, and she stayed.
Charlotte: Sarah came back to check on her, and then they heard gunshots.
Charlotte: They followed the noise to a playground where dead bodies were lined up.
Charlotte: The bodies weren't of infected, and while Charlotte was examining the scene, Sarah saw a small girl run off and followed her.
Charlotte: She followed her all the way down to a dark subway station.
Charlotte: She was attacked and the little girl disappeared into a door.
Charlotte: Charlotte noticed she was gone and ran after her to help.
Charlotte: She pulled her out of there and they returned to the asylum, where it appeared Tim had become infected.
Charlotte: Charlotte desperately tried to get him to fight his hunger, but she couldn't, and Sarah shot him.
Charlotte: Charlotte was upset, so she ran off, back down to the subway station where Sarah couldn't follow because of all the infected.
Charlotte: She then found the door and talked to a man behind it for awhile, who said he couldn't open it for her because of some "code"
Charlotte: She eventually got frustrated and just tore it off its hinges with her inhuman strength, and almost got him killed as infected poured in.
Charlotte: They went into another room and locked it, and it turned out she had stumbled on some underground cult-civilization run by people just like her.
Charlotte: They offered for her to stay, insead of killing her, as the man that she had been talking to had implied would happen.
Charlotte: She asked if she could bring Sarah, and they said yes.