Girl, Missing

Girl, Missing is an English-language young adult thriller novel by Sophie McKenzie, published in 2006.
It won the 2007 Bolton Children's Book Award, the 2008 Manchester Book Award and the 2007 Red House Children's Book Award for Older Readers, as well as being longlisted for the Carnegie Medal.
It was also one of the books picked for the Richard & Judy Children's Book Club.
Plot.
Part One: Finding Martha.
The main character is 14-year-old Lauren Matthews,who lives in London with Lydia and Dave, and their son, Rory. Lauren is doing an essay for homework which is called 'Who Am I?'. It suddenly strikes Lauren that she doesn't know her true background. Eager to find out about her past, Lauren goes on a website called Missing-Children.com, and finds an American girl named Martha Lauren Purditt, who went missing less than two months before Lauren was adopted! 
Lauren's friend, James 'Jam' Caldwell comes around and Lauren tells him about the information she'd discovered on the website. After comparing the photograph of Martha with a photograph of herself as a toddler, and then one of herself now with an age-progressed photo, Lauren notices that she and the missing girl look alike, which led her into believing that she might be Martha Lauren Purditt.
That night she hears her adoptive parents talking about her downstairs saying they will let her see "the diary" when she is 16 years old that will tell her information about her adoption. A few days later she goes into the attic discreetly, looks through the diary, where she finds that she was adopted from Marchfield Adoption Agency in Vermont, run by Taylor Tarsen; also noted down is the name "Sonia Holtwood".
After persuading her family to go on a holiday to a theme park in America, they travel to America, leaving her dad behind for work issues and taking Jam in his place. While Lauren's mother and Rory are waiting to change planes, Lauren and Jam sneak off without anyone knowing and get a plane to Burlington, Vermont.
Once the plane lands, Lauren and Jam get a bus to Marchfield, (where Lauren was adopted) and meet with Taylor Tarsen, the owner of the agency. He refuses to show Lauren her adoption file, but when Lauren mentions Sonia Holtwood, Taylor tells Lauren she was looked after by Sonia before she was adopted, and gives her $150 so she and Jam can stay in a motel. Jam informs Lauren that he found out where Lauren's adoption file is, and the two stay in a motel for the night.
That night, Lauren and Jam break into Marchfield Adoption Agency and find Lauren's adoption file, but all that is in it is an address on a scrap of paper. Lauren and Jam then get a taxi to the address. When they arrive at what they believe to be Sonia Holtwood's flat, they discover that Sonia moved out years ago but that an young, good looking woman called Sona that still lives there. She remembers when Sonia was there, invites them Lauren and Jam into her flat as she has recognised Lauren's face as used to babysit Lauren when she lived in the flat with Sonia. Sona tells Lauren that as a toddler Lauren rarely smiled, but looked pretty when she did. On one of these occasions, Sona attempted to photograph Lauren but Sonia came bursting in, furious and left with Lauren the day after.
Lauren and Jam set out to find Sonia. They run into a female police officer named Suzanna Sanders, who offers to take them on a ride in her car. Lauren accepts, but Jam is doubtful. However, after a brief discussion with Lauren, he decides to come with her. Once in the car, Suzanna gives them orange juice, which was drugged and both Lauren and Jam begin to feel sleepy, so they drift off. Hours later, they wake up and find that their phones and belongings have been taken away. Beginning to feel suspicious, they ask Suzanna where they are and demand to be let out of the car. It is from here when she reveals her true identity: Sonia Holtwood. Lauren also finds out that Sonia is a hostile woman who took Lauren away from her real family at the age of 3. Sonia then dumps them in the middle of nowhere and takes off with their phones and belongings.
Luckily for the pair, a man called Glane rescues them and takes them to his log cabin. Glane then takes them to Boston, where he works. Lauren goes on the internet to find out more about Martha Lauren Purditt. She discovers that Martha's parents were Annie and Sam Purditt who live in Evanport. Seeing her determination to go there, Glane offers to take her to Evanport.
Part Two: Finding Lauren.
Arriving at her destination, Lauren meets the Purditts: Annie, Sam and their two daughters (and therefore, Lauren's sisters) Shelby and Madison. When Lauren tells them that she thinks she might be Martha, Annie is the only one who believes her, while the others are sceptical. They consider taking a DNA test, to see if Lauren is really part of their family.
Meanwhile, Lauren's adoptive family visit her and confess that they didn't mean to steal her from her real family; they adopted her legally, as they had no idea that she was a stolen child, but thought that she was Sonia's child and Sonia gave her up for adoption. The DNA results confirm that Lauren is indeed the daughter of Annie and Sam Purditt. Although they are her biological parents, she doesn't really fit in with them, except for Madison. She learns from her parents' lawyer that her adoptive family have been accused of abduction and are in prison. Still missing her adoptive family terribly, Lauren has a row with Annie, accusing her that Annie doesn't love her. Annie replies that she almost stopped living after Lauren went missing.
After Lauren moves in with Shelby and Madison, her two sisters, she sees that Annie is a bit extreme in her emotions. Lauren likes Sam much better than Annie, but the person she likes best is her grandmother, who understands her much better than either of her parents. Lauren also realises that her sisters' personalities seem to be the opposite of each other: while Shelby is rude and has a lot of attitude as doesn't seem to get on with anyone in her family, including Lauren. Madison is a sweet and innocent girl that quickly came to view Lauren as much better sister than Shelby. When Shelby starts bullying Madison, Lauren stops her and comforts Madison. Moments afterwards, Lauren receives a text message on her phone, supposedly from Shelby, telling her to keep quiet or die. She receives another of these later.
One day when Lauren was making hot chocolate she spots someone at the door. She does not know who it is until they take their hood down and she realises it is Jam and lets him in. He proposes that they run away together but Lauren hesitates and says that she needs time to think about it. She, Jam and Madison all go down to the marina so they can talk. Jam gets angry when Lauren says that she does not want to leave her real family, and storms off. Then she gets another text. She thinks it's from Shelby, but it's actually from Sonia Holtwood (who also sent Lauren the other threatening messages that she thought they were from Shelby), saying that her sister will die unless she goes to Sam's boat, the "Josephine May". There, she finds Madison gagged and Sonia with a paid criminal called Frank. Later, Madison annoys Sonia by pretending to have a stomachache ache. She gets hit by Sonia, sending her flying across the room and causing her to crack her head on a hard shelf. Sonia and Frank then leave the boat, after Lauren lies to Frank saying that she hasn't got her cellphone. Madison and Lauren have been wedged into the room by Sonia and Frank, but then Jam appears and rescues them. The boat starts to sink as they are still trapped inside. When Jam has rescued them Madi is unconscious. 
The next chapter is in the hospital, where Madison has still not awoken after smacking her head. Annie and Lauren are with her when she awakes, and the two share a true mother–daughter moment, where Lauren sees Annie for who she truly is. Back at Sam and Annie's house, Lauren meets her adoptive parents at the door; they say that they have been released from jail and have been invited there by Sam and Annie. All of them have a conversation and Lauren is asked who she wants to live with: her birth parents or her adoptive parents. She replies that she chooses both.
Epilogue.
Lauren says that she now partly lives with Sam and Annie, and that she spends the school term in England with her adoptive parents. Jam is now her boyfriend and often comes with her to Sam and Annie's, and Shelby has stopped mocking her or Madison. Lauren adds that she never spends more than a few weeks away from either family, and she ends by saying that she was asked to write another 'Who Am I?' essay. She then says that it was easy because she finally knows who she is. In the essay she writes "girl, found" and writes about both families.
Characters.
Lauren Matthews/Martha-Lauren Purditt/Lauren Purditt
The adoptive daughter of the Matthews and the biological daughter of the Purditts. The biological sister of Shelby Annabelle Purditt and Madison Gloria Purditt. When she was 3, Lauren was kidnapped by Sonia Holtwood. She was on the beach (Long Mile Beach) with Annie playing hide-and-seek with a red bucket the day she went missing. Later on in the book she has flashbacks of that day, her first flashback was with Carla (Jam's mum) during a hypnotherapy session.
James "Jam" Caldwell
Lauren's best friend, who is 15 and goes with her on her journey. He later becomes her boyfriend. His mother (Carla) spends no time with him, being too busy with his younger siblings or her job. Jam got a PSP when he was younger from his father. He made 6 grooves in the back of his PSP, Lauren asked about it multiple times during the story, he says it's 'nothing' but later explains to her he that he carves one in for every time he has spoken to his dad, every time he has promised to see him but hasn't.
Carla cadwell
Jam's mum who is divorced with Jam's dad, she doesn't spend time with Jam as she is usually working as a therapist or worrying about her other children in England London.
Madison "Madi" Purditt
Lauren's youngest sister, aged 6. She is Lauren's favourite sister.
Shelby Purditt 
Lauren's other younger sister, aged 13 (one year younger than Lauren). She is a bully who doesn't get on with her sisters. 
Sam and Annie Purditt
Lauren's biological parents who live in south America.
Dave and Lydia Matthews
Lauren's adoptive parents who illegally adopted her. They are from England London. 
Rory Matthews
Lauren's younger adopted brother, born through IVF. 
Mr. Taylor Tarsen
A worker in the Marchfield Adoption Agency who helped 'Sonia Holtwood' sell Martha Lauren Purditt to the Matthews when she was 3. 
Sonia Holtwood/Marcia Burns
The kidnapper who took Lauren at the age of 3 at Long Mile Beach where she was playing hide-and-seek with her mother. Sonia later sold her to the Matthews. Sonia changes her appearance all the time; she has many different looks. She then again kidnapped Her and Jam and then again her and Madi.