Mary and her twin sister Jessica Drake were born on December 18, 1965, with Mary being born first. Mary stated that they didn't get along because Jessica was jealous of her and tried to turn everyone against her.
It was considered by the doctors that her mental health issues started to show up when she was a teenager, after an incident involving a child that was under Mary’s care. Jessica was babysitting Teddy Carver when she phoned Mary to come and takeover so she could go out with a boy. The baby died under mysterious circumstances while Mary was taking care of him and as a result she was sent to the Radley Sanitarium. Mary told them she hadn't even touched the boy and it was Jessica's fault, but no one believed her. Mary dated Ted Wilson when he was a senior in college. However, Mary was being admitted on and off at Radley, and she vanished from Ted’s life without an explanation, she chose not to tell him that she was pregnant. Mary later gave birth to their son, Charles Drake, inside the asylum. He was adopted immediately afterward by Jessica and Kenneth, who feared that Charles might be in danger under his mother's care. Mary stated that she never got the chance to hold Charles, as her sister took him before she could.
A few years later, after she was either released or escaped from Radley she entered a restaurant and saw Peter Hastings. She posed as her sister, Jessica - who Peter had an affair with before, and slept with him, which led to her having a second and third child. The first, Spencer Hastings, was taken in by the birth father, Peter Hastings, and his wife Veronica. However, Mary kept the identity of the second child a secret and allowed for Dr. Cochran to arrange the adoption in exchange for half the money from selling the baby, the money helped gain her a permanent release from Radley. The youngest twin, Alex Drake, although taken, would live a troubled life.
The woman was permanently released from Radley at 28 years old. Not much is known about her whereabouts from this period of time, only that she'd traveled a lot, especially in Europe and Latin America. She once tried to find her daughter Alex but was unsuccessful.
At some point, Mary's returned to Rosewood and after Charlotte's death, she sided with "Rollins", Charlotte's doctor and secret lover, and the unknown person named A.D. to avenge her daughter and to obtain the Carissimi Group's money. After she was betrayed by Archer, she did all she could to protect Spencer and, by extension, Alison. She took the blame for Archer's death and remained in jail before being found and released by her other daughter Alex Drake.
After conspiring with her to kidnap Spencer, she and Alex are kidnapped by Mona and placed in her own version of A's Dollhouse in France until the two escape at point before the Pretty Little Liars: The Perfectionists and is now on the run.
Personality wise, Mary seems to be a first-class manipulator and an intelligent woman. Because of her mental health history, she can also be described as unstable and willing to do anything that's necessary to retrieve what is rightfully hers, even if that means backstabbing her own family.
"All laboratory and test results are normal. The patient is introverted and will not speak to anyone. The patient has random violent outbursts, lashing out and throwing objects."
Mary Drake was initially institutionalized for an incident involving the death of a child who was under her care while she was babysitting. Mary was forced to stay in Radley until she was 18. After that, the woman was readmitted several times until she got out permanently at 28 years old.
When Spencer is looking out of her window, Mary sneaks in behind her and goes over to another part of the room when Veronica comes in. Mary's shadow can be seen leaving the room without Spencer or Veronica noticing.
Ali wakes up in the hospital with a vision of what appears to be her dead mother, and concludes she is dreaming because of the concussion. "Mrs. DiLaurentis," tells her everything is going to be alright and Elliott loves her and will protect her.
Hush, Hush, Sweet Liars
Ali wakes up from a nap to the sound of a music box playing, and envisioned what appears to be her dirty, dead mother watching her in the bedroom. Immediately after, she receives a call from someone sounding like Mrs. DiLaurentis and asking: "Did you miss me?".
Ali shares her hospital dream with Emily, as well as the new vision, which Emily thinks was a side effect of her pain medication. As she sleeps again later, Ali has a nightmare of Dt. Wilden in bed with her. Over the phone, Elliott says her mind is just playing tricks on her due to "misplaced guilt", but she keeps having visions of both her dead mom and Wilden.
On election night, Ali disappears from her house, and Emily finds her crying and shaking in the church, saying that her mother and Wilden "came back" for her and they are going to take her straight to hell. Thinking she is unable to tell what's real anymore, she voluntarily checks herself into Welby State Psychiatric Hospital at the same place Charlotte had been held, against Emily's wishes.
The same night, Spencer and Toby are breaking into the secret room at Radley. They are interrupted by Mona, who joined them in what was seemingly an empty room, until she found old medical records for a woman named Mary Drake, who had a child named Charles Drake while she was a patient 30 years ago. Jessica and Kenneth adopted Charles as Mary was unable to take care of him.
Looking over footage from the cameras Caleb had keeping surveillance outside the Lost Woods Resort, the Liars are shocked to see what looks to be Mrs. D by the fence he had built, asking themselves how this is possible.
At Ali's house, "Wilden" rips off his mask revealing himself to be Elliott, and Mary Drake, who is revealed to be Mrs. D's twin, joins him. They succeeded in committing Alison, and with her hospitalized, Elliott has the Carissimi Group's money and the house, as they're trying to avenge Charlotte's death. Elliott states he was in love with her and Mary always felt an attachment as her birth mother. She tenderly glances at a photograph of Charlotte and says this is what she would've wanted.
While they're trying to come up with a plan regarding Hanna's abduction, The Liars, Toby, Ezra and Caleb see Mary going to the police station. When Toby goes to interrogate her, he finds out Mary's Jessica twin sister and she's there to report a break-in at the Lost Woods Resort, her newest acquisition.
Thinking she's "A.D.", they go to spy on her and investigate the motel, only to find out she had bought everything it's needed to cover up a murder.
Later, Mary visits the Hastings residence and is invited by Spencer inside, at a cup of tea. She, then, tries to subtly interrogate Mary, finding out the woman knows her family suspiciously well. Spencer asks why her existence should be considered a secret, question by which Mary feels offended. She apologizes immediately after, telling Spencer she can be rather overly sensitive at times. Before she leaves, Mary asks how did Spencer know that she's living at Lost Woods Resort and Spencer quickly comes up with a lie.
Driving her car, Mary encounters an abused Hanna over the road. She stops the car and they exchange looks.
Mary drives Hanna to Spencer's home, at her request. Later that day, she visits Spencer again at her workplace to find out if Hanna is okay. After some questions posed by Spencer, the woman says how she had ended up in Radley, stating the only person to blame was Jessica because she manipulated all of them.
Visiting Radley to unlock old memories, Mary encounters Emily and they start talking about Alison and her health issues. Mrs. Drake assures Emily that Dr. Rollins is professional and thinks there is nothing to worry. They decide to pay Alison a secret visit at Welby, through.
There, both of them discover that Alison's mental state is getting worse, as she seems to be delusional, thinking Mary is her mother. After Elliott discovers their presence, he starts arguing with Mary about their plans, as she thinks Elliott is crossing the line on Alison's mistreatment.
Hit and Run, Run, Run
She visits Alison at Welby and informs her that it will be alright and that she's in charge now.
Along Comes Mary
Aria welcomes Ali back home and learns that Mary is Alison's supervisor while she is not on the care of the psychiatric hospital.
Mary reveals that Elliott contacted her when she was London, and he reported that Charlotte had been murdered. When confronted by Alison for letting Elliott torture her, Mary says she was vulnerable, but she did not know his real intentions having cut strings after he revealed himself.
Alison later tells Mary that all her money is gone, and Mary says he backstabbed her.
Wanted: Dead or Alive
Spencer and Alison leave The Brew and join Mary at the DiLaurentis' house, where Det. Marco Furey is, wanting to give some answers about Archer Dunhill - Eliott's real identity.
In the Lost Woods Resort, Spencer tries to break in the building, but is surprised when Mary shows up with a crowbar, thinking that she was Elliott trying to kill her. They start talking about Elliott/Archer.
Mary claims she and Charlotte never met. When Charlotte (then Charles) was born, Jessica immediately took him from her, never letting Mary even hold the baby. Alison then reveals to her that Charlotte previously used the alias of CeCe Drake, and Mary gets emotional.
In the DiLaurentis house, Mary and Alison discover that Jason has returned to Rosewood, but Jason soon expels Mary out of the residence, stating that Alison's health is now under his care. Following, Alison argues with Jason and asks him to take a chance to meet Mary. Anyway, Jason is still certain that Mary has bad intentions.
At the Brew, Jason enlists Aria's help to make Alison see who Mary really is. Jason then reveals that Elliott also completely diverted the Carissimi Group's money.
In Jenna's room at the Radley, Spencer and Hanna spies on Noel Kahn hiding Mary Drake's old Radley Sanitarium file, which he has stolen from Toby's house, inside a box. They also catch him calling a Dr. named Cochran, as he says he is impatient and out of time.
Back at dinner in the DiLaurentis house, Jason argues with Alison, saying Mary's not a good person, not even a way to replace their mother, Jessica. Then, Mary tells them and Aria about the day she saw Jason in years. In a flashback, Jason appears in Carol Ward's house, and Jessica quickly dispatches him. Through the window, Mary sees him and is crying. Jessica complains about Mary being there, and Mary says she is worried about what really happened to her then deceased child—Charles—, but Jessica tells her Charles had died under her care and expels Mary. Back in the present, Mary says that, when Jessica decided that a conversation was over, it was over. Mary then talks about Jessica spending a lot of time down in a storm cellar at their Aunt Carol's house, and Alison and Aria grow suspicious.
Alison, Emily, Spencer, and Hanna arrive at Carol Ward's house and they find the hidden cellar. Inside, within a Mary Drake file, Spencer discovers that Jessica was in charge of Mary's mental health and that she had authorized electroshock therapy. In another file, Emily discovers that Mary had a second child while she was hospitalized in Radley Sanitarium and that this child would have the same age as them. They then begin to think that this child — cousin of Alison — may be behind "A.D." mask and be wanting revenge for something.
Exes and OMGs
Spencer and Aria get together to find Dr. Cochran, with whom Noel was talking to the day before, and discover that he was responsible for the birth of both Mary Drake's children when she was hospitalized in Radley Sanitarium.
The Wrath of Kahn
Aria joins Jason in a deep research inside Mary Drake's past. They find out that someone manipulated the adoption files of Mary's second child, but, nonetheless, they discover that Noel's father, Steven, was responsible for the adoption, leading Aria to believe that Noel is Mary's second child.
The DArkest Knight
After kidnapping him, Hanna uses a knife to get some of Noel's blood to send to a DNA lab to find out if he really is Mary's second child. Hanna is shocked when she discovers that Noel is not Mary Drake's second child, and reveals to her friends what she really had been up to.
The Liars are sent an address that leads them into an abandoned school for the blind where Jenna, armed with a gun, attempts to murder the Liars with Noel. Unknown to all, Mary is hiding there.
Noel accidentally kills himself and Jenna then shoots at the Liars, as they run, but get separated from Spencer, who is shot. Before Jenna could cause more damage, she is taken down by Mary and pulled away by "A.D." unseen.
The Liars go up stairs where they find out Mary holding and singing to a wounded Spencer, and start accusing her of having something to do with this. Mary then tells Spencer she would never hurt her and reveals that she is Spencer's biological mother, leaving them shocked as Spencer passes out in her arms.
Spencer is woken up by a paramedic who asks for her name, and then her mother's. This leaves Spencer confused, as it was just revealed to her that Mary Drake is her birth mother. At the hospital, the Liars asks themselves how Mary ran away after she revealed being Spencer's biological mother.
One week later, Spencer looks for Mary in the Lost Woods Resort, but is unsuccessful.
At the police station, Spencer and Marco talk about Jenna and her connection to Noel and Archer. He then pulls out a gun in an evidence bag, and asks Spencer is she's sure it was the gun that shot her. Spencer says yes, but Marco tells her that it is not the correct gun, and that Mary Drake and Jenna Marshall could've been at the school for the blind the night Noel died.
Spencer arrives home and finds out that Veronica has returned to check on her. Veronica asks how she feels, and Spencer says it all depends on how things go in the next few minutes. Veronica becomes confused, and Spencer confronts her about Mary being her birth mother. Veronica confirms this, and says that Mary tricked Peter into thinking she was Jessica, resulting in a baby about to grow up in a sanitarium; then, Veronica turned to Judge Kahn — Noel Kahn's father — and adopted the child, as Veronica felt that it was the right thing to do.
Later in the barn, Spencer gets a text from "A.D.", saying that if she wants to learn more about Mary that she has to play the game board they sent.
After completing her task, Spencer returns to the barn and a letter from Mary Drake comes out of a slot in the game as a reward for playing it. She then gets the letter, which was written in Radley before she was born, with the words 'For my child' on the front. She reads the letter from Mary, where she apologizes for what she's done.
These Boots Were Made for Stalking
Spencer asks Marco to track down Mary Drake and shows him the letter Mary wrote for her.
Later Spencer requires her father's presence at home, ending up arguing once again with her mother about Mary Drake.
While searching for Mary, wanting answers from her, Spencer and Hanna run into Pastor Ted's house, and he tells them he doesn't know about her whereabouts. After the girls leave, Mary shows up behind Ted (revealing she's been hiding there) and he asks what she is really doing there.
Peter returns home and Spencer confronts him about hiding the truth about Mary from her.
Later, Ted visits Hanna at Lucas' loft and reveals to her that Mary was hiding at his house recently. He reveals that he knows her because they dated years ago, which resulted in Charlotte's (then Charles) birth.
After seeing Spencer's efforts, Peter tells her that Mary is dangerous and recalls the last time he saw Mary: Mary dressed up like Jessica, and sneaked into the Hastings residence and went to Spencer's bedroom so she could see her daughter all grown up.
Trying to make Spencer stop from searching Mary, he reveals that Mary killed Jessica for revenge for hiding that Charles was alive the whole time and that he had become Charlotte.
Driving Miss Crazy
She appears from inside Spencer's car an they head to the Lost Woods Resort. She tells Spencer that she is leaving and wants Spencer to go with her. Her reasons being that she wants to make up for lost time and save her from the crazinees of Rosewood. Spencer politely turns her down, not wanting to leave her family, but acknowledges that Mary is dear to her.
Farewell, My Lovely
She gives Spencer and Alison the Lost Woods Resort as a means for them to pay for their lawyers should they be arrested again. When the Liars are arrested by the police for Archer's death, Mary intervenes and lies that she did it. She also confesses to Jessica's murder, saving the Liars from a murder charge. As she is arrested, Mary signals the girls, particularly Spencer, to remain quiet thus sparing them a prison sentence and ending A.D.'s game.
'Til Death Do Us Part
Mary is seen being visited in prison, apparently by “Spencer” (Alex using Spencer’s name). Alex asks for Mary’s help with something. She is next seen in Alex’s Bunker after Spencer wakes up in a cell and injects her with something to knock her out. Mary later tries to have lunch with Spencer and states that until Alex came to visit her several weeks ago she had no idea where she was or if she was even alive. She explains how she sold Alex to a wealthy couple in England in exchange for money that helped pay her way out of Radley permanently. However she discovered that Alex’s adoptive parents had abandoned Alex at an orphanage because she had “issues” and had run away from there a year before Mary found what happened. Mary opens the cell to hug a tearful Spencer before closing and locking the door again but Spencer was able to take one of Mary’s hair clips to pick the lock. When Alex tries to kill Spencer, Mary attempt to talk her out of it but Alex knocks her out before she can interfere. When Alex is taken away by a cop, he states that they found Mary several blocks away and have her in custody. It’s revealed that the cop was actually Mona’s boyfriend and Mary and Alex are now being held in Mona’s own version of the Dollhouse in France.