Mary was a character introduced in Series One, Episode Two. She is an Irish teenager who became pregnant when she came to London. She is portrayed by Amy McAllister.
At 15, Mary ran away from her home in Dublin, Ireland, after her alcoholic mother took a man to live with them. Hitching rides from truck drivers, Mary eventually found her way to Poplar. Homeless and without any skills, education or trade to keep her fed, Mary went hungry for days. One day while scavenging bread crumbs left for the birds, Mary was approached by the mysterious Zakir, not knowing he was a pimp.
After being charmed, given food and wine to drink, Zakir lured Mary to bed, and gave her first pleasurable sexual experience. By morning Mary was so in love with him that she prostituted herself for him.
Mary worked the streets, sometimes bringing men back to the brothel, and collecting coins from her customers. After being with three, sometimes four men a night, Mary got pregnant. After a terrifying event, where another prostitute was forced to have an abortion, where Mary had to help hold her down and where she saw the aborted foetus in the chamber pot in their room, Mary hid her pregnancy from everyone, knowing if she was discovered she would be forced to abort as well.
One night, when Mary was about 5 months pregnant, Mary did not cover up her protruding belly in front of one of the other girls working at the brothel. The girl softly tells Mary she can and will have to "do things" and that "they won't" let her keep it. The next morning, Mary sneaks downstairs while Zakir and his friends are in the next room, stealing money from a coat pocket and fleeing the brothel.
However, the money she took was a £5 note, too much money for a girl like her to spend without people getting suspicious. She fears if she is looked at twice, someone will tell Zakir where she is and what she did, and he will take her back to the brothel by force and make her abort her baby.
Standing outside a cafe, Nurse Lee passes by and Mary stops her, thinking she looks like a high-class sort of woman who could have change for the note. However, she doesn't and so Mary asks her to change the note inside the cafe for her. After initially refusing, Jenny notices the small belly beneath Mary's coat and agrees to go into the cafe with her, buy her a meal with the note and pay for it so the owner will think its hers.
After eating, Mary opens up to Jenny about her past. When Jenny notes that she can see Mary is expecting a child, Mary is slightly panicked, but calms when she learns Jenny is a nurse and midwife. Upon learning that Mary has nowhere safe to sleep, Jenny takes her back to Nonnatus House where she promises to help her talk to Sister Julienne in the morning.
The next morning, Sister Julienne explains to Mary that she must leave to a safe house set up by Father Joe for former prostitutes. Mary begins crying and refuses to leave. Sensing that Mary is terrified of something, Sister Julienne gets out of Mary what happened to the other girl and her baby at the brothel. After a bit more gentle prodding and assurances, Mary agrees to go if Jenny goes with her.
At first, Mary is extremely closed off and nearly hostile with Father Joe, knowing she's bound to be judged for her actions by a member of the church and a man at that. She explains how she came to Zakir, and that he's her boyfriend. Father Joe says he knows she was forced and says there's no shame in it. Mary replies, bitterly, "Not for the men". Jenny leaves the house and Mary stays.
A few weeks later, Jenny is checking in on Mary, now near the end of her pregnancy. Mary gushes over the first night she met Zakir and Jenny snaps at her that what Zakir did to her was "obscene, not beautiful," and that she shouldn't speak or think of him. Mary then reveals that he's standing out in the street, and that he's been coming there everyday. Not wanting Mary to fall back into Zakir's trap, Father Joe sends her away to a mother and baby home in Kent. Before leaving, Jenny gives her her scarf, one which Mary admired.
A while later, Mary, now noticeably better dressed and healthier, is visited by Jenny after having her child. Mary has a daughter, who she named Kathleen, meaning "pure". She explains to Jenny that first seeing her daughter was like she'd "missing her [my] whole life".
Some time later, Jenny receives a letter from Mary, stating that the baby was gone and to come quickly. Arriving back at Father Joe's, Jenny consoles a distraught Mary, screaming for Kathleen. Due to not feeding Kathleen and not receiving care to dry up her milk, Mary gets abscesses in both her breasts. After confronting Father Joe for allowing this to happen, he explains that she's only 15 and is not fit or ready to be a mother and cannot provide for herself, let alone a child. He says she can be employed without a baby, and have a new life, get married and have another child. Jenny asks him if he thinks that will console her, to which he replies "it consoles me". Jenny tends to heartbroken Mary and helps bind her breasts to stop milk production. After the infection is cleared, Mary leave Father Joe's safe house.
At the end of the episode, Jenny in voice over reveals that Mary was never reunited with Kathleen, and though she would look for her, "her name would not be Kathleen anymore".
Mary's only other appearance was in Series One, Episode Four. After having her child taken from her, Mary's mental health broke down very quickly and she snatched the Redmond's newborn daughter Gillian from her pram outside her house.
It is revealed that Mary has gone back to prostituting herself, though she is not under a pimp, and is homeless. She takes to calling Gillian "Kathleen". Mary becomes very frustrated when a screaming Gillian refuses to feed from a bottle, smashing the milk against the wall in anger. At night, she leaves Gillian alone in a crate covered with cardboard and "goes to work". The police track her down after she is caught trying to steal a pint of milk. Constable Noakes asks Jenny for help and she rescues the baby and Mary is arrested.
However, when it is seen how her heartbreak over her own child drove her over the edge, Jenny and the nuns try to plead for leniency for Mary. Sister Julienne and Sister Evangelina go to talk to the Redmonds, but Mr Redmond refuses to help, saying Mary would hang if he had his way. When Sister Evangelina points out that Mrs Redmond is the only one to know of the pain and anguish Mary went through losing her own daughter, Mrs Redmond agrees to talk to the police about mercy for Mary.
Mary is last seen in a prison cell, Jenny trying to talk to her, but receiving no response from Mary, who seems to have been rendered catatonic by the trauma of losing "her" child again. It is not known what became of her after this.