Harry Potter and the Half-Blood Prince is great in mysteries and also it had solved some of the questions that were asked by the characters since the first book and it was altogether a great way to fill the gap between the dark lord finally showing himself to the world and his absolute rise in power.
The book starts off normal as anyone would do but Harry then notices the strange behavior of his school rival and decides to find out more and during the year Harry is having secret lessons with the headmaster where he learns more about the dark lord as in his motive and a way to defeat him.
When Harry and dumbledore go out to find one of the things that would lead them to victory but come back to find out that the school is being attacked by death eaters who Harry’s school rival Draco Malfoy had brought in and now he was being forced to kill the headmaster but Harry’s most hated teacher professor snape does it instead and he flees leaving harry more motivated than ever to end the dark lord once and for all.