This fic is based upon the MOVIE version of "The Prime of Miss Jean Brodie", released in 1969, and starring Maggie Smith and Robert Stephens. The screenplay was co-authored by Muriel Spark (the author of the book) and Jay Presson Allen. I own nothing except this idea.

Jean Brodie must be stopped, thought Sandy Stranger as she walked down the familiar hallways of the Marcia Blaine School for Girls. She had spent her "impressionable" years here, with that ridiculous woman and her pathetic "set," her "fascisti," of which Sandy had been a reluctant member. It was not Sandy's fault, after all, because Jean Brodie was an expert at manipulation. She had killed Mary MacGregor, and did it so skilfully that no one but Sandy ever suspected her guilt. Not even Jean herself. While Mary was stupid, that only made that woman's machinations all the worse. She was our teacher! Sandy thought, she was supposed to protect us, not cause us harm! Her memories of this school only served to fan the flames of her anger that had first ignited when Jean Brodie chose Sandy to be her confidante.

Jean Brodie had told Sandy of her plan to put Jenny in Teddy Lloyd's bed as a proxy for herself. She used to say, "Sometimes I feel as though Jenny was a part of myself," as if to justify her disgusting plots. And while Sandy was always, to Jean Brodie, her dependable Secret Service, in truth, Sandy told her almost nothing. She never told her when she became Teddy's lover instead of Jenny. And when she ended her affair with Teddy, it was because she finally realised the powerful hold that Jean Brodie had on the people around her – it was witchcraft.

She knocked on Miss Brodie's classroom door and found her collecting the books from her previous class.

"Ah, Sandy, my dear! I have hardly seen you at all this past week. I have some important things to discuss with you regarding Jenny. Will you join me for tea?"

Sandy made an effort to keep an expression of composure, like the Mona Lisa.

"Yes, Miss Brodie," she replied, and took the books from her teacher's arms to store them in the cabinet, under the spot where her reproduction Giotto fresco used to hang.

Jean Brodie gathered her cloak and books together before turning off the lights and shutting the door behind them. They walked together to her bicycle, to which she strapped the books in the wicker basket that was attached to the rear. They walked to her flat, Jean questioning Sandy about the goings-on of her set, Teddy's portraits, and Jean's current class.
When they arrived at Jean's flat, she put away her books while Sandy busied herself in the kitchen making tea. She carefully filled the sugar bowl with the cubes of arsenic she had made – luckily, Miss Brodie always took sugar with her tea, while Sandy never did. As she brought out the heavily laden tea service, Miss Brodie told Sandy,

"I think that Teddy and Jenny will soon be lovers. Everything you have told me indicates that they will."

Sandy maintained her expression of composure with difficulty, replying, "Mr. Lowther is getting married to Miss Lockhart."
Miss Brodie's hands, which were holding the heavy teapot, trembled. Handing Sandy's filled cup to her, she took the sugar tongs and placed one of the arsenic cubes in her tea, before responding, "I was the one who encouraged Mr. Lowther in his reluctant pursuit of Miss Lockhart."

Sandy, pleased when Jean took a sip of her arsenic-laced tea, said, "Do you think you are Providence? Do you think that you can ordain love? Jenny will not be Teddy Lloyd's lover. I am."

"Whatever possessed you?" her teacher asked furiously, placing her teacup on its saucer with such force that the china rattled.

"Why does it matter to you which one of us it is? It does not matter to Teddy! He painted my portrait, and it does not even look like me! Even the skin tones are yours! He is obsessed with you – no, not obsessed, bewitched! Bewitched by an impossibly ridiculous woman!"

"How dare you speak to me in that manner!" her teacher said, standing up with difficulty.

"I suppose I always knew that you would ask me 'how dare I.' I dare because you will no longer corrupt young minds. You will no longer teach – not at Marcia Blaine, or anywhere else. You are finished."

"You cannot stop me from being who I am – I am a teacher, first, last and always! Even if I were to receive a proposal tomorrow from the Lord Lyon, King of Arms, I would decline it! I am dedicated to my girls! If you want to stop me from teaching, you will have to assassinate me!"

Sandy smiled coldly. "I have, Miss Brodie. Don't you notice the difference even now? Who would have thought that arsenic could resemble sugar cubes so closely? Within a few minutes, you'll be dead – and you will do no more harm to anyone."
Sandy picked up the sugar bowl and Jean's cup before gathering her cloak. Opening the front door, she called over her shoulder, "Goodbye, Miss Brodie!"

As she walked down the stairs, she heard the door reopen and Jean Brodie cry, "Assassin! ASSASSIN!"

The door leading to the outside closed, and Sandy went on her way. Jean Brodie collapsed at the top of the stairs, the echoes of her words ringing in her ears for all eternity.