Emma Becker
Sutton's twin sister and a girl who has moved from foster home to foster home despite being initially adopted by a rich family in Beverly Hills. She switches places with Sutton to escape accusations made by her last foster brother. Is the nicer and more thoughtful twin.
- Adaptation Name Change: In the books, her name is Emma Paxton.
- Cool Big Sis: Is a much better sister than Sutton to Laurel.
- Foolish Sibling, Responsible Sibling: The Responsible to Sutton's Foolish.
- Polar Opposite Twins: Is much less outspoken, nicer and generally more thoughtful than Sutton.
Sutton Mercer
The adopted daughter of the Mercers and Emma's twin sister. She lived happily as a rich girl in Phoenix until she discovered she had a twin after coming home from a trip to Paris, she decides to go to LA and look for their biological mother.
- Alpha Bitch: Played with, she has some of the characteristics (Popular, Manipulative and wants to be Homecoming/Prom Queen) but she doesn't care enough to truly become one.
- Brilliant, but Lazy
- The Chessmaster: Sutton was already shown as quite the chessmaster but the season finale revealed that she was collaborating with her mother Rebecca.
- Foolish Sibling, Responsible Sibling: The Foolish to Emma's Responsible.
- The Glorious War of Sisterly Rivalry: With Emma and Laurel.
- Heel–Face Turn: She eventually comes to realize Rebecca can't be trusted and decides to help Emma.
- Polar Opposite Twins: Is more manipulative, outspoken and much meaner than Emma.
- Posthumous Character: In the books, she is dead, but her spirit watches over Emma as she tries to figure out who killed her.
- Spared By Adaptation: But She's very much alive in the show.
- Girly Girl: To Emma's Tomboy.
- Preppy Name
- Rich Bitch
Madeline "Mads" Rybak
- Ambiguously Brown: Her actress' heritage is a mix of ethnicities/races.
- Big Brother Worship: Is very close to Thayer.
- Hot for Teacher: Her dance teacher to be exact, her father was not amused.
Thayer Rybak
Alec's son and Mads' older brother. He is keeping the twins' secret and helping them solve their mysteries. Was an Unlucky Childhood Friend for Sutton but recently developed feelings for Emma.
- Dogged Nice Guy: To Sutton.
- Face–Heel Turn / Evil All Along: Which is true, nor his motivations will never be revealed
- Fake Guest Star
- Preppy Name
- Secret-Keeper
- The Smart Guy
Laurel Mercer
Ethan Whitehorse
Sutton's boyfriend who ends up falling in love with Emma.
- The Big Guy
- Race Lift: In the books, he's the blond-haired, blue-eyed, astronomy-nerd Ethan Landry.
- Secret-Keeper
- Sibling Triangle
Ted Mercer
Sutton's adoptive father and birth father of Laurel. Is married to Kristin and best friends with Alec. He has several secrets, several revolving around both Annies and Justin.
- Luke, I Am Your Father: He didn't know about Emma though.
- Preppy Name
Kristin Mercer
Sutton's adoptive mother and birth mother of Laurel. Is married to Ted and oblivious of many of his secrets.
- Heroic Safe Mode: In the finale, after Rebecca confirms her fears of her and Ted's affair, she switches to Heroic BSoD when Ted makes his speech at the engagement party.
Alec Rybak
The Phoenix District Attorney and father to Mads and Thayer. Can be controlling and may have some secrets. Is best friends with Ted and beginning a relationship with Rebecca Sewell.
Annie 'Rebecca' Sewell
- Big Bad
- Sutton And Emma I Am Your Mother: She only tells Sutton though.
- Man Behind the Man
Char Chamberlain
One of Sutton's True Companions. She's initially suspicious of Emma's actions in Sutton's place, but eventually embraces it as a new direction in their friendship.
- Demoted to Extra
- Locked Out of the Loop: Was initially worried about this when her friends started keeping secrets from her, she gets better.
- Put on a Bus
Nisha Randall
An ex-friend of Sutton's who is technically the series Alpha Bitch, she's not as profilic as her character type is on other shows. She still seems to want to be friends with Sutton and is mean to her as a means to get her back for whatever she did.
- Advertised Extra
- Alpha Bitch
- Demoted to Extra
- Race Lift: In the books, Nisha (whose last name there is Banerjee) is Indian. In the show, she's African-American, with the last name Randall.
- Rich Bitch
Justin Miller
Laurel's first official boyfriend and a golf jock. He pretends to be as wealthy as the other Arroyo but is actually secretly living in a foreclosed home. He tells Laurel that his parents dies years ago in a car crash but later in series it's revealed he has ulterior motives.
- Becoming the Mask
- Beta Couple: With Laurel
- Jerk Jock: Averted, he's pretty nice.
- In Love with the Mark
