The series follows a pair of troubled teenage girls, and their encounters with a dangerous supernatural force that may or may not be the answer to their problems.
After Evie Grayson witnesses a murder committed by drug dealers, she is targeted by local crime lord Sebastian Polk. She discovers a mysterious ally in the forest, the titular Birch — a fierce guardian that will destroy her enemies when summoned. But as gruesome deaths plague the small town, Evie begins to question the nature of her supernatural protector.
In a parallel story, Lanie Bouchard is the adopted daughter of a local politician and has just given birth in secret. Her parents insist the baby is her "sister", and go to increasing extremes to keep Lanie away from her child. Troubled by strange visions and a power she doesn't fully comprehend, Lanie fights to save herself and her daughter from the Bouchard's control.
The series was renewed for a second season, which aired on March 26, 2021 and concluded on May 28th of the same year.
The Birch provides examples of:
- Abusive Parents:
- The Bouchards are extremely controlling of Lanie, drugging her and locking her inside the house to prevent her from acting out.
- In Season 2, Rory's father had been abusive towards her.
- Accidental Murder: The Birch goes after Rory's mother while the woman is tied to a chair. It makes mushrooms sprout out of her forehead. When Rory tries plucking them, her mother goes into convulsions and dies.
- Bait-and-Switch: It appears at first that both segments chronicle the Birch protecting two people, Evie and Lanie. But then it's revealed that Lanie isn't protected by the Birch, she is the Birch, having originally been a human capable of controlling plant life and eventually transformed into the titular creature when her powers skyrocketed in a bout of grief.
- Children Are Innocent: Gavin Polk is a typical 10-year old boy, seemingly unaware of his family's criminal empire. Thurston actively works to keep it that way.
- Death of a Child: Lanie's newborn daughter Laura is poisoned by the Bouchards with nightshade. Subverted in that Laura comes back to life of a sorts.
- Humans Are the Real Monsters: Very much the case in Season 2, where the titular monster is ultimately just a tool for the season's true villain, Rory, who deliberately summons the Birch and uses it as part of a murder spree against her tormenters.
- Jerk with a Heart of Gold: Thurston Polk works for his uncle selling drugs, and is the initial antagonist of the story. But his POV reveals that he tries to spare Evie out of guilt for her mother's death, and is working on a plan to escape from his abusive uncle.
- Mama Bear: Lanie will do anything to protect her newborn daughter, including killing the doctor keeping her captive. Likewise, the Birch functions as one to her summoner, attacking those who harm Evie in the first season and Rory in the second.
- Meanwhile, in the Future : The series jumps between the stories of Evie and Lanie, one in modern times and one decades prior, who both have a connection to the Birch.
- Missing Mom: Evie's mother died of a drug overdose prior to the series. The Polks provided it, creating the initial conflict between the Polks and the Grayson family.
- Misaimed Fandom: In-universe. Evie becomes Rory's greatest hero because she sees Evie, (who was falsely blamed for the murders committed by the Birch) as somebody who took matters in her own hands and paid back those who caused her pain.
- My Secret Pregnancy: Lanie's parents took her out of school for "Mono", and kept her at home until she gave birth. Afterwards, they actively try to convince her that the new baby is her "sister".
- Red Baron: Evie eventually gets nicknamed the King's Point Killer by the public due to the Birch's brutal murders being blamed on her.
- The Reveal: Why Lanie's parents keep her child away from her: when Lanie was a little girl, her mother was pregnant and told her that she was going to have more responsibilities with a new brother or sister. Unwilling to share her mother, Lanie had the vines attack the woman, making her miscarry and leaving her infertile.
- Self-Made Orphan: Lanie uses her powers to first kill her father by ripping off his jaw. After her daughter's death, she initially seeks comfort in her mother's arms. But when her mother says it was better that way, Lanie starts her transformation into the Birch and ends up constricting her mother to death.
- Sympathetic P.O.V.: Thurston comes across as a dangerous thug initially, but the episodes from his POV often show him in a much better light.
- Tragic Monster: Lanie becomes the titular Birch, consumed by her rage and grief at the death of her daughter.
- Tragic Villain: Rory was abused by her father. Her mother did nothing to stop the abuse. An embarrassing picture posted by her mother goes viral and earns her the Embarrassing Nickname of Mary Mayonnaise. After she sends a picture of herself in bra and panties to a boy who pretends to like her, he sends it to everyone in school.
- Would Hurt a Child:
- The Birch captures Gavin and buries him in the garden, though it isn't clear whether she would have killed him or not. Evie has considerable difficulty getting him back, once she realizes her mistake.
- Sebastian Polk, on the other hand, has absolutely no issue with hurting his nephew. One of his goons threatens to slice up Gavin's face on his orders, and when Gavin defies him to save Thurston, Sebastian slashes the child with a power saw and kicks him several times.
- In Season 2, Evie threatens to hurt Undead Child Laura as a way to control the Birch.