Magic, love, death, darkness, violence... the quest goes on...

An exciting scene from the story forms the cover of the book. Dumbledore and Harry, wands out, in the middle of a fire-storm.
The sixth an darkest adventure with Harry Potter and his friends so far.
Romance and jealousy play an important part in this volume, though not center-stage, that place is reserved for Lord Voldemort alias Tom Riddle. Masks are off and the queste to find Voldemort shifts into a higher gear. For once Harry and Dumbledore team up for a secret mission, and that does not bode well for someone.
Fleur stuns the Weasleys to her credit and embarrasment of the red-headed family.
Snape finally (?) shows his true colors, Malfoy shows he still has some human feeling inside him.
Hardly anything is funny in this book although friendship can give a warm feeling.
The title refers to an annotated textbook for Potions that Harry acquires. It help him to get better marks than Hermione who finds this dishonest but also dangerous. The only hint Harry has to whom this book originally belonged and who wrote thos extremely useful remarks is his signature; the Half-Blood Prince.
Rowling starts working to the end of the story which will last one more book. She takes this quite literally and the question pops-up at breakfast: "anybody we know died today?"
The author builds tension throughout the book, tension that is relaxed a bit after some exciting and most often violent action. More background is added to the characters while relations between them are explained by the psychology of the individual.