Harry Potter and the Chamber of Secrets: Novel

Ron joked that Tom Riddle could be the one who killed Moaning Myrtle; he’s right.
Draco Malfoy teased Harry about having Ginny as his girlfriend. They later become an item.
In Goblet of Fire, Percy Weasley started dating Penelope Clearwater. She is the victim of the Basilisk.
In Half-Blood Prince, Draco Malfoy uses a necklace to try to kill Dumbledore. It is first seen in the Chamber of Secrets when Harry is in Knockturn Alley.
In Half-Blood Prince, Draco Malfoy uses the Vanishing Cabinet to transport the Death Eaters. It is first seen in the Chamber of Secrets; Harry is hiding in it when Draco Malfoy and his father come by. Nearly headless Nick persuades Peeves to destroy a cabinet, the one used in Half-Blood Prince.