This is part three in a six-part series.
Part 1 (1-5) can be read
here. Part 2 (6-10) can be read
here.
Chapter 11
Hermione's Helping Hand
A certain character from the Knight Bus is arrested suspected of relating information about Death Eaters. One character is removed from Hogwarts by her parents. Dumbledore is frequently absent from the school. A character persistantly flirts with Ron.
Quidditch tryouts are held and 3 new players join the team. The trio visit Hagrid who is a bit offended they didn't take COMC. He tells them Aragog is unwell. The Draco issue is further discussed following raids on the Malfoy mansion.
Chapter 12
Silver and Opals
Harry tries some of the spells invented by the 'Prince' which are recorded in the book. Predictably, Hermione disapproves of this activity. They discuss how they feel negative about him and the possibility that it could've belonged to a Death Eater.
They make their first visit to Hogsmeade. Harry gets into a scuffle with Mundungnus who is, as usual, up to no good. Although this time, it's personal.
An incident happens and Katie Bell is rushed to the Hospital Wing.
Chapter 13
The Secret Riddle
This is the second of Harry's lessons with Dumbledore and they once again take a trip into the pensieve. They witness 11-year-old Voldemort. The child likes to be alone and hates being associated with others. Unusually for his age, he is able to control his powers and use them to have power over people.
Chapter 14
Felix Felicis
Harry acknowledges that something appears to be happening between his friends. Unfortunately for Ron, he catches his sister in a rather compromising position with one of his classmates. This stirs up emotions in Harry. Ginny makes some revelations about Hermione & Krum which horrify Ron. Ron decides to return the affections of a previous flirt in retaliation. In return, Hermione seeks her own revenge.
Chapter 15
The Unbreakable Vow
Love potions are discussed in some depth. A transfiguration class leaves many emotionally wounded. Hermione is ironically comforted by an unlikely friend. Harry asks Luna to go with him to Slughorn's Christmas Party. Hermione invites one of Ron's rivals to go to the party with her. Harry eavesdrops on Snape and Draco discussing a plan which makes him even more suspicious of both of them.
Continue to part four (chapters 16-20) 
HBP Chapter-By-Chapter: 11-15 (spoilers) 
"You tell those spiders, Ron!" 
