This is one of my favorite books.

If Harry in the Muggle world conjures awaits him a hard time at Hogwarts. When Voldemort also penetrates his thoughts and he is taught by his enemy, he put a club with his friends. To give everyone a chance that they learn self-defense.

That may be the thickest book in the whole series, but again like nothing. J.K know again to keep the tension well, so you just do not want to stop reading.