Lia Zhang

She is apart of the Naturals Program. Not a lot is known about Lia's backstory because she is not forthcoming about it. She often uses her powers of deception to mask the truth of her words or the feelings behind them. From what Cassie learns of before Lia joined the Naturals she has killed a man, and was part of a cult.

Natural Skills
Lia is a natural lie detector, though the ability was honed by her upbringing. She can tell if a person is lying or telling the truth, by studying facial expressions and their voice. She is an excellent liar herself. She is respected and semi-feared by all the other kids because she is able to tell if they are lying.

History
Lia and her mother risked getting deported, as they were in America illegally, so a person involved in a cult found them and, to Lia's mother, this was a savior. Lia grew up in a cult, surviving by saying she had visions from God. She killed a man when she was nine. There is no mention of her father.

She is bilingual and ran away from home when she was young. She was living on the streets when the FBI found her. Soon after that she joined the Naturals program and was the second student (the first was Dean). She and Dean became like brother and sister in the time they had together alone.

Her real name is Sadie.

Books
Twelve It's revealed that she has become a civilian FBI consultant.

Michael
Michael and Lia have an off-and-on-again-relationship, which works best for the pair. This is mostly because they both have similar personalities, which draws them together, but is also the reason that they don’t work out long term. While at the beginning of the series the two are off [again], at the end of the series they are together. It's implied that their on-and-off-again relationship continues into adulthood.

Cassie
==== Lia feels threatened by Michael's attachment to Cassie, while Cassie is threatened by Lia's demeanor and snark. Even though she views Dean as a brother, it's hard for her to accept him relying on Cassie instead of her. Lia and Cassie's friendship starts off rather rocky, but with time they start to have a better understanding of each other, though they do have more of a love/hate relationship than, say, Lia and Sloane. ====

Dean
Lia and Dean became like brother and sister in the time they had together alone before others joined the Naturals. Her trust in him grew after Dean accompanied her by running away after she had first joined the program. They consider each other family and will almost always confide in each other. Dean is also extremely protective of Lia, and he definitely acts as the older brother. He is also one of the only people that she will actually listen to. She cares more about him than anyone else.

Sloane

Lia is very protective of Sloane and views her as a sister. Lia is always one of the first people at Sloan’s side when she needs it. She also stands up to anyone who tries to bring Sloane down. Sloane feels left out when she's not included, like when some of the others sneak out to college party to investigate a crime. Sloane knows that before Cassie showed up she would have been included, so afterward they work on including Sloane more.

Trivia

 * While Lia may seem like she is a party girl, she is very smart [though not as smart as Sloane].
 * She has a very different style of fashion compared to Cassie, mostly because she tends to use her clothing and outward appearance as a shield to protect her inner feelings.
 * Her real name is revealed to be Sadie during a game of Truth or Dare.