The final book in the Harry Potter series is markedly different from the other six. Rather than return to Hogwarts for their final year, Harry, Ron, and Hermione drop out of school to focus on finding the Horcruxes and destroying Lord Voldemort. 
 The book is fairly evenly divided into two parts. In the first, the friends have their mettle tested. They are given ample reason to doubt Dumbledore and find themselves without any real way forward on the path that he's set them on. On the other hand, they find out about the Deathly Hallows, which could be used to make them stronger than Lord Voldemort. 
 In the second part, the battle between Dumbledore's Army and Voldemort's forces wages over Hogwarts. 
 The Deathly Hallows is the culmination of the message of love and friendship that has been so central to the series. Harry must put his faith in Dumbledore despite the evidence, and he must be willing to die for his friends just as his mother once died for him. As Dumbledore says, "If there is one thing Voldemort cannot understand, it is love" - and only this power can conquer him. 
 It's a lovely, if occasionally problematic, message.