Hermione is generally portrayed as a rule-follower and someone who studies hard, wanting to excel in class and happy to let her schoolmates know that she is smart. In fact, she is a bit of a know-it-all at times. In Harry Potter and the Chamber of Secrets, however, Hermione acts in ways that seem out of character for her by breaking the rules and encouraging Harry and Ron to join her in a highly risky plan to discover what goes on in the Slytherin common room.

Hermione is the instigator in this book. When a teacher explains the history of the Chamber of Secrets to the class, the three friends learn that Salazar Slytherin constructed the hidden Chamber of Secrets and that it contains a monster that could wipe out all non-pure blood wizards. This is likely one reason that spurs Hermione to go against her customary behavior and violate multiple Hogwarts rules.

She concocts a plan to brew a polyjuice potion so that the three can masquerade as Slytherins and spy on Malfoy. Hermione asks a teacher to allow her to check out a library book from the restricted section, where she has no borrowing privileges, another move that is out of character. Hermione also risks sneaking into Professor Snape's office to steal ingredients she needs for the potion. All of these moves are completely at odds with the personality of Hermione we have seen up until this section of the story.

Perhaps the reason that she is willing to risk getting caught breaking the rules is because the monster living in the Chamber of Secrets is tasked with killing all non-pure wizards, and Hermione is the offspring of muggles, or human mortals. Perhaps another reason that she risks getting caught is because Malfoy has insulted her publicly, calling her a "mudblood," a pejorative name for a mixed-blood wizard. Hermione does not want to get caught by the monster. She also wants to be viewed as being equal to her fellow school mates. Her animus towards Malfoy is probably another reason why she is willing to act so against character.

One of Hermione's many strengths is her ability to understand difficult textbooks and class lessons. She, Ron, and Harry read through the book to learn to make the polyjuice potion, but it is only her ability to parse through the difficult instructions that allow them to advance the plan.