Madeleine "Maddy" Young was a senior house officer on the hospital's Acute Assessment Unit and later Keller ward.

Time at Holby City Hospital (2007-09)

Maddy arrives at Holby City Hospital in episode "Face Value". It is revealed that she has a history with General Surgical Consultant Dan Clifford, and that the pair are good friends. The pre-existing relationship between Maddy and Dan initially makes some staff wary of her, especially on the hospital's Acute Assessment Unit, where she is assigned. However, she quickly strikes up a friendship with PRHOs Matt Parker and Dean West, and Senior Staff Nurse Donna Jackson.

Maddy engages in a one-night stand with Cardiothoracic Surgical Registrar Sam Strachan in episode "The Borders of Sleep", and later bends the rules to help him take care of underage prostitute patient Jade MacGuire. In episode "What Lies Beneath", Maddy's father arrives in Holby having escaped from prison. She treats him for an injury he sustained prior to escaping, and, aided by Dan, helps him avoid the police when they arrive searching for him. Her father reveals to Dan that Maddy once stole pharmacy drugs and planted them on the abusive boyfriend of her twin sister, Hannah. She discusses her past with Dan, mentioning the fact she once covered for him when he operated drunk. Maddy gets into further trouble when she poses as Cardiothoracic Consultant Elliot Hope, attending a racial awareness course under the guise of "Ellie", only to be caught out by the hospital's Chief Executive Officer Jayne Grayson.

Maddy's sister Hannah arrives at Holby with an abscess in episode "Guilt by Association". Maddy convinces her to have an operation by illegally stopping her pain medication, in order to emphasize how badly she needs surgery. In the following episode, Hannah seeks out Maddy's help when she accidentally gives her daughter, Sunny, a methadone overdose. Although Maddy again breaks the rules and the law to help them, Sunny dies while being treated from an exacerbated pre-existing cardiac problem. The police are suspicious of Sunny's death, but Dan blackmails fellow Consultant Ric Griffin into covering up for Maddy. Dan and Maddy go on to share a short-lived romantic relationship before his departure in October 2007. She is hurt by Dan's love for his sister-in-law Louise, and left heartbroken when Dan departs Holby for a prestigious job in France. In episode "Love Will Tear Us Apart", Maddy makes an error in the middle of an operation after Dan calls her out of the blue to arrange a meeting. She is devastated when he later stands her up.

Following Dan's departure, Maddy goes on to support Sam through his battle with Non-Hodgkin lymphoma, and form a professional relationship with the new head of the AAU, Linden Cullen. When Linden is suspended following the death of a patient, Maddy breaks the law by stealing samples from the hospital's morgue to prove his innocence. She is severely reprimanded by Jayne Grayson, although Linden is eventually cleared. When Linden becomes involved with a case of conjoined twins, Maddy is temporarily placed in charge of the AAU in his absence.

Maddy had recently been transferred to Keller on surgical rotation. She continuely tried to impress Ric. But Ric kept taking his frustrations out on her because she was friends with Tom O' Dowd. But Ric was impressed in the end and offered her a promotion and told she could be a great surgeon one day.

In "Mirror, Mirror" Maddy's sister Hannah, having been released from prison, arrives at Holby with her cellmate Chantelle, who has been stabbed, in her car. Because Chantelle refuses treatment in the hospital, believing they will send her back to jail for being in a fight, Maddy agrees to treat Chantelle in secret. Linden finds out and tries to help and they operate on her but Ric finds out and tells her to report it to the police. She refuses as doing so would cause Chantelle to run away, leaving her with a potentially fatal stab wound. As a consequence Ric withdraws her from the promotion interview.

In "Seeing Other People" Chantelle stabs Maddy in the back, whilst she was on her way to Ric Griffin to talk about the promotion.

In "Just a Perfect Day" Maria finds Maddy stabbed and bleeding out on the floor in the Keller ward toilets. She immediately starts trying to resuscitate her. Linden rushes in to help. Three weeks have passed since Maddy was stabbed. She is in Holby Care and we hear her thinking about a letter she has written to her sister Hannah. She seems to be fully recovered and is desperately trying to get back to work and be interviewed for the ST3 job. Ric held the interviews open until Maddy was well enough, and today she's going to make sure she gets the job. Maddy's going to show them that they can throw anything at her and she'll cope...even after being stabbed. Linden wants Maddy to be careful and take things easy, as she nearly died, but Maddy wants to get back to work.

Meanwhile, Maddy receives a visit from Dan Clifford, who she has not seen for over 18 months since he took his job abroad. After hearing about Maddy's attack he has arrived to see how she is doing and to offer her a research position with him at his new hospital. Maddy decides to try for the position at Holby before making any decisions.

Back on the ward, a father and his two daughters have been brought in, one with a stab wound and one badly burnt. The father only has minor injuries but the police seem to believe he had something to do with the incident. Maddy tries to find out what is happening from the father, who is not talking to the police. She seems to have some connection with him but can't seem to put her finger on what it is.

Ric is having second thoughts about allowing Maddy to be interviewed. He explains to Michael that he doesn't think that she is ready for the position. Maria overhears the pair's conversation and chips in saying that she feels that Maddy is perfect. Michael knows Maria is right but Ric thinks he might have made a mistake and he explains to Maddy that he is withdrawing her interview offer. Maddy is devastated.

Clifford comforts Maddy and explains that the board have now asked him to move back to Holby and there is a position waiting for him. After advice from Linden Maddy decides to stay at Holby. Her aim is to show Ric what she is capable of achieving. Determined to show Ric her skill she takes a leading role in the procedure on the stab victim. Ric is impressed but explains that he would like to see more before she gets an interview. Her plan has failed.

Maddy overhears Ric and Clifford talking about her. Clifford explains that Ric might be hit with a lawsuit if he denies Maddy an interview and suggests that he interviews her without giving her the job.

The stab victim dies and Maddy blames herself, even though there was nothing she could have done. But Ric tells Maddy he has reconsidered and she can have an interview. Although she's happy to have this opportunity she knows that Ric is only doing it to avoid a court case.

She heads into the interview, bold and honest about her work. She impresses the board and they give her the position. She can't believe it. She heads out to tell Dan Clifford the news, who then tells her that the board have offered that he can move his entire work to Holby and he tell her that the reason he wants to stay is that he loves her. Maddy is overjoyed and they kiss passionately against the bonnet of his car. She heads back to the ward to find the father of the stab victim missing. She finds him in the basement, confused and he speaks to Maddy as if she is his dead daughter. Maddy tries to help but he keeps referring to Maddy as his daughter. At the end of the episode, it is revealed that everything that happened since Maddy was stabbed was actually a dream and that Maddy actually died in Chantelle's attack. This whole episode was Maddy living out her perfect day in her head. On October 21, 2009, Chantelle was admitted to AAU, pregnant after her boyfriend kicked her in the stomach. Despite telling Maria she didn't kill Maddy, she actually confessed to the murder after Mark told her of the consequences about her lying about her boyfriend abusing her and killing Maddy.