In preparation for a visit from Uncle Vernon Dursley (Richard Griffiths)'s client, the Dursleys lock Harry (Daniel Radcliffe) in his room. There, Harry finds Dobby the house elf (voiceToby Jones) who warns against returning to Hogwarts. When Harry refuses, Dobby frames Harry for ruining Vernon's meeting. Furious, Vernon traps Harry in his room to prevent his return to Hogwarts. Ron (Rupert Grint), Fred and George Weasley arrive in their flying car to rescue Harry and take him back to The Burrow, their home. Harry meets Ron's younger sister, Ginny (Bonnie Wright), who is beginning Hogwarts and has developed a crush on Harry. Harry also meets Ron's parents, Mr. (Mark Williams) and Mrs. Weasley (Julie Walters). Soon after, Harry and the Weasleys travel to Diagon Alley by Floo Powder. Harry accidentally mispronounces "Diagon Alley", and lands in Knockturn Alley. Fortunately, Hagrid (Robbie Coltrane) happens upon him and reunites him with the Weasleys and Hermione Granger (Emma Watson). While shopping, Harry meets Gilderoy Lockhart (Kenneth Branagh), a famous wizard and author, and later Draco Malfoy (Tom Felton) and his father, Lucius (Jason Isaacs), who praise Voldemort and deride Harry, Hermione and the Weasleys.



At King's Cross Station the Weasley family, excluding Ron, cross through the magical barrier to Platform 9 3/4 with ease. Harry and Ron find they cannot go through (Dobby sealed it to prevent Harry's return to Hogwarts); as a result, they miss the Hogwarts Express. Harry and Ron manage to reach Hogwarts with the flying car, but accidentally land in the school's Whomping Willow, which breaks Ron's wand and causes the car to act erratically. The car ejects the boys and drives off by itself.



Ron and Harry are able to begin Hogwarts normally, but Harry begins to hear an ominous voice that no one else can hear. Harry, Ron and Hermione find the message The Chamber of Secrets has been opened. Enemies of the heir, beware written in blood across a castle wall and discover caretaker Argus Filch's cat has been Petrified. The Chamber of Secrets is a chamber which can only be opened by the Heir of Slytherin; it is said to be the home of a monsterous creature that will only obey the Heir. Harry suspects the Heir is Malfoy. To interrogate him, the three brew Polyjuice Potion to disguise themselves as Malfoy's friends Crabbe and Goyle. They learn Malfoy is not the heir and that he does not know who it is.