Father Joe was an Irish priest who appeared in Series 1, Episode 2 while Jenny dealt with Mary's case.
Father Joe had opened a Home for women and young girls who'd been exploited by men into prostitution. He understands why women are lured into prostitution by men who show them some kindness, offer some affection and make the feel good and loved, and it appears to anger and revolt him, though he is not disgusted by the women he takes in, only by the men who take advantage of them.
When Jenny Lee met Mary, a 15 year old pregnant runaway, who had been pushed into prostitution by her "boyfriend" Zakir, Sister Julienne opted to send Mary to live in Father Joe's Home for former prostitutes, which is a transition house of sorts. Mary initially refuses out of fear that Zakir will find her and make her abort her baby. Sister Julienne says that when she goes to Father Joe's she will be in the community and therefore, she will be safe and have the midwives to care for her.
Upon arriving at Father Joe's, he brings them tea and fig rolls. Mary immediately says she is not a "fallen woman" and goes on to explain how she came under Zakir's control. Father Joe assures her that they understand she didn't enter into prostitution willingly, and assures her there is not shame in what she was made to do. Mary snaps that there's no shame in it for men.
Later, as Father Joe and Jenny go over Mary's paperwork alone, they discuss how Mary ended up a prostitute. Father Joe explains that "it's a pimp's trick, old as the hills. A young man finds a vulnerable girl, lures her to bed with a kiss and kind words. By the time he's finished with her, she'd do anything for him." He says this bitterly, as he's likely seen this same scenario dozens of times before.
Jenny inquires how the girls can be so easily overcome, and Father Joe answers it is usually because they've been in danger all their lives, and often lived without or with very little love, affection or kindness. He tells her that most of the girls who come through his House have suffered poverty, not only of the physical sense, but also of the emotional sense, which has left them unable to differentiate between love and abuse.
Sometime later, Mary leaves Father Joe's establishment when Mary reveals to Jenny that Zakir has been standing outside her window every afternoon. Father Joe vows that he will send Mary as far away as he has to to get her out from under Zakir's influence. He says because Mary is so young and because she isn't "sharp in the head", she is too valuable an asset for Zakir to give up. Father Joe arranges for Mary to be sent to a Mother and Baby home in Kent, where she remains until she gives birth, and until her baby is apprehended weeks later.
After Mary's infant daughter was taken from her, Mary is next seen at a new establishment, neither Father Joe's Home, or the Kent hospital. Mary is devastated at the loss of her child, and Jenny Lee is furious at Father Joe.
Upon finding that Mary has infections in both her breast from not being able to nurse her baby so abruptly, Jenny blows up at Father Joe. When questioned why he allowed the child to be taken from it's mother, Father Joe plainly states that it was in the child's best interest, as Mary is 15, without family, without a home, without an education and no trade skill of any kind. When challenged that Mary gave up prostitution, he replies that Mary doesn't "have that choice" implying there's a good possibility she would slip back into prostitution even if they let her keep the child. He tells Jenny she isn't the only one whose angry about the situation.
Father Joe tells her because Jenny is young, God will forgive her for her "righteous indignation" and that God and the church both forgive sinners (in reference to Mary). He goes on to say that Mary is young and without a baby, she is employable. He says she could find love, move on and have another child.
Jenny asks if he thinks that sentiment will console Mary, to which he replies "It consoles me."
Mary leaves Father Joe's not long after, and is never reunited with her baby.