Following the plan perfectly during Potions class, Harry heaves a [firecracker] into Goyle's [cauldron] while Hermione nips into Snape's office to steal the ingredients needed for [Polyjuice Potion]. Snape is irate, but does not directly accuse Harry, and the trio successfully adds the ingredients after class.

One morning in the [entrance hall], an announcement appears for a [Dueling Club] - so Harry, Ron, and Hermione sign up.

Gilderoy Lockhart starts the first [Dueling Club] meeting with a demonstration, where he makes a fool of himself demonstrating with Snape. They soon have the students divide into pairs to practice.

With [Dueling Club] members paired up, Lockhart has them begin, but the students (Harry and Malfoy included) attack with much more than the requested [Disarming Charms].

Snape suggests Harry and Draco model how to block spells. Lockhart's demonstration fails but he sets them at it anyway, and Draco, at Snape's suggestion, launches a snake at Harry, a situation exacerbated when Lockhart launches it into the air. When the snake slithers toward Justin Finch-Fletchley, Harry yells at it to stop, but doesn't understand when Ron and Hermione promptly drag him from the room.

Ron and Hermione confront Harry about being a Parselmouth, and after some explaining, convey the gravity of the situation. Harry learns that Salazar Slytherin was a famous Parselmouth, and that there have been very few since - and therefore, that he will now certainly be thought the [heir of Slytherin].

With Herbology cancelled, Harry heads around the school to look for Justin and explain what happened at the [Duelling Club]. He doesn't see him but finds some Hufflepuffs in the library discussing why Harry must be the [heir of Slytherin]. He confronts them, but with no success.

Harry, leaving his confrontation with the Hufflepuffs, briefly runs into Hagrid, holding a dead [rooster], in the hall. Hagrid realizes something is wrong but Harry won't tell him what, instead heading off to Transfiguration.

Walking alone in the hallway, Harry accidentally discovers a [Petrified] Nearly Headless Nick and Justin Finch-Fletchley in the hall. Peeves soon arrives and screams for help, attracting the whole school, and Professor McGonagall whisks Harry away.