Hermione Granger, played by Elizabeth Bennet, is a rookie private detective, has teamed up with Harley Quinn to form H&H Dective Agency. They just completed their first case, solving the blackmailing of Ron Weasley by Draco Malfoy. As they investigate, their styles can clash but they get results. Along the way, Hermione is drawn to Harley's carefree and playful nature, leading to a blossoming friendship and potential romance? After the success of their first big case, word is getting around. Hermione arrives and announces they have a new case, only to discover Harley carefully building what looks like a confetti bomb in their tiny office in a closet in the back of antique shop to find. Hermione is worried it will destroy the office. Hermione explains they have a new case, her former Professor Mcgonagall is missing her cherished brooch and believes it was stolen.

Harley Quinn and Hermione arrive at the prestigious private school Hogwarts, where Hermione went to school, to investigate the theft of Professor McGonagall's brooch. Harley observes how fancy the school is and compares it to her own humble upbringing and gets a little self concious.

Harley Quinn and Hermione review their notes from the interview Professor McGonagall, who revealed that her stolen brooch was a symbol of her Order of Merlin. Professor McGonagall showed them where it was stored in a glass case in her always locked office. They asked Professor McGonagall who might want to steal the brooch as it does not have any monetary value. Hermione looked for other entry points and her keen eye noted some red and yellow fibres caught in the air vent cover, pointing to a Gryffindor theif! Harley starts using different nicknames for Hermione, including Hermy, Mimi, Puddin

Hermione and Harley decide to pay a visit to the Gryffindor common room to see if they can gather any information about the thief, with Harley insisting on going undercover as a student because Hermione would be recognized as a famous alumni.

Harley practices her Australian accent with Hermione but saying a few famous Australian expressions. Hermione is unconvinced but Harley goes ahead. Hermione waits anxiously outside the Gryffindor common room while Harley, in her ridiculous disguise, tries to gather information from the students.

Harley, still in her ridiculous disguise, tries to blend in with the Gryffindor students. Hermione communicates with her via bluetooth headset to tell her what to say. Hermione tells Harley to ask about the latest quidditch match, who are the best teachers, what people think of this professor mcgonagall? She hears she is a real tough professor. Her attempts at subtlety are foiled when she accidentally knocks over a plate of treacle fudge, causing a commotion.

Harley and Hermione review their findings from the Gryffindor common room, with Harley revealing that she managed to swipe a suspicious-looking parchment from one of the students, which appears to be a cryptic message about the theft of Professor McGonagall's brooch.

Hermione and Harley decide to investigate the Gryffindor students who were in the common room when Harley was there, starting with a student named Franklin Longbottom, Hermione's friend Neville's son, who seemed nervous and fidgety when Harley asked about Professor McGonagall.

Hermione and Harley review their notes from the interagation of Franklin Longbottom. They learned that one of the senior students in Gryffindor put out a bounty on Professor McGonagall's brooch, because she gave him a bad grade on his NEWT exams. He decreed that the first year students had to steal it or they would be cleaning bathrooms for a month, so Franklin did the heist. Franklin agreed to return the brooch to Professor McGonagall and admit his part in the plot.

Hermione and Harley return the brooch to Professor McGonagall, who is relieved and grateful, and then they confront the senior student who put out the bounty, revealing his scheme to the entire school and earning him a stern punishment from the Headmaster.

Hermione and Harley celebrate their second successful case. They discuss how it was George Weasley's daughter Roxanne who was behind the bounty was duly punished. Harley reveals that she's really enjoying being detective, but mostly because she gets to work with Hermione. Hermione says she enjoys working with Harley. Harley remarks that she's disappointed that Hermione didn't wear any cute costumes this time, making Hermione embarrased. Harley says Hermione is adorable when she is embarssed.