The Harry Potter movies removed several important details surrounding Lucius Malfoy’s plot in Harry Potter and the Chamber of Secrets, ultimately affecting Voldemort’s overall Horcrux plan. Though the film does reveal that the Malfoy patriarch was responsible for Tom Riddle’s diary falling into Ginny Weasley’s hands, it does not provide the reason for which he did it—or the consequences he faced from Lord Voldemort as a result.
In the Harry Potter and the Chamber of Secrets movie, Harry and the Weasleys ran into Lucius and Draco Malfoy at Flourish and Blotts. When rewatching it a second time, it’s easy to see Lucius drop Tom Riddle’s diary in Ginny’s cauldron. Later, Harry speculated as much and even confronted the Death Eater on his actions after the memory of Tom Riddle that emerged from the diary was destroyed. Lucius admitted what he had done. His disregard for the life of a young girl (or those at the school) established him as a purely evil character, but what was his reason?
Lucius Malfoy Hoped Tom Riddle’s Diary Would Hurt Arthur Weasley
In the Chamber of Secrets book, the scene at Flourish and Blott’s went a little differently. It became clear through the interaction that Lucius Malfoy held a significant grudge against Arthur Weasley since the latter had created several laws that made it harder for wizards to own dark objects, especially those intended to fool and harm Muggles. To avoid jail, Lucius Malfoy had been forced to secretly sell several of his belongings (which Harry accidentally witnessed while he was in Borgin and Burkes in Harry Potter).
So, Lucius Malfoy concocted a plan in Harry Potter that he hoped would get Arthur out of his way. He happened to have a diary that, though he didn’t fully understand, would result in the opening of the Chamber of Secrets. He planted the powerful Dark object on Ginny Weasley, hoping that her involvement in the murder of Muggle-born children at Hogwarts would reflect poorly on Arthur Weasley and that he would lose his job. This would leave the despicable Lucius Malfoy free to own all the Dark objects he desired without pesky Mr. Weasley threatening his high status in the wizarding world.
Tom Riddle’s Diary Was Different Than The Other Horcruxes
There is another big question that the Harry Potter movies never explain: how did Lucius Malfoy end up with one of Voldemort’s Horcruxes to begin with? Harry Potter and the Half-Blood Prince and Harry Potter and the Deathly Hallows explain that Voldemort wouldn’t have just left his concealed soul fragments lying around for anyone to find. So, why was the diary different? Albus Dumbledore explained in Half-Blood Prince that Voldemort had a different plan in mind for his diary Horcrux than the others, and Lucius Malfoy was supposed to be a part of it.
Since Lord Voldemort had been forced to close the Chamber of Secrets before the events of Harry Potter, he set up a plan to one day open it again. He made his diary into a Horcrux and saved it until it was the right time to plant it back at Hogwarts and allow it to finish its Dark work of eliminating the Muggle-born witches and wizards. Sometime before his downfall at the Potters’ cottage, Voldemort gave this diary to his trusted servant, Lucius Malfoy. He didn’t tell him what it was—only what it would do. He also instructed him not to use it until he was ordered to. So, Lucius kept it and waited.
Lucius Malfoy Was Severely Punished For Using The Diary In Harry Potter
Lucius Malfoy kept Voldemort’s diary safe for a decade. Still, when he began to face pressure from Arthur Weasley’s department at the Ministry of Magic in Harry Potter, he decided it was time to act. By this point, he had assumed that his Dark Lord would never return. Therefore, he was not afraid of the consequences of using the diary when Voldemort had instructed him not to. Understanding very little about what it actually was, Lucius used it for his gain. When Voldemort returned and discovered his diary had been destroyed, he was enraged.
Dumbledore told Harry in Half-Blood Prince that Tom Riddle’s diary had been his first clue that Voldemort had created a Horcrux and that there was likely more than one. It was clear to him that the diary was meant to be a throw-away item—so Voldemort must have made backups. Dumbledore also learned through his intel (likely Severus Snape) that the Dark Lord had severely punished Lucius Malfoy for using the diary without permission. This could only have been because the diary had been more valuable than Lucius realized.
Why The Harry Potter Movies Cut The Diary Horcrux Details
Though readers of Harry Potter and the Chamber of Secrets didn’t know it yet, Tom Riddle’s diary was the first clue that Lord Voldemort had created Horcruxes. It was the single essential detail that tipped Albus Dumbledore off to the idea that the Dark Lord could have created more than one Horcrux, which no wizard in existence had ever done. Still, the Harry Potter movies cut most of the diary’s details, including Lucius Malfoy’s motivations for using it and how this affected Voldemort’s plans.
This is because, in the end, Lucius Malfoy’s movie counterpart didn’t need a reason to be evil. He was the Dark father of Harry’s least favorite classmate, and that was enough. Additionally, since the Horcruxes were a new concept to audiences in Harry Potter and the Half-Blood Prince, the film could get away with not explaining why Voldemort would have left the diary with Lucius, and Horace Slughorn’s memories were enough to establish the fact that Voldemort’s soul was in seven total pieces. Still, the details of the Harry Potter books told a far more cohesive story, something the films are doomed to do without.