All is not well in the wizarding world; Voldemort has returned and The Order of the Phoenix is in disarray. At Hogwarts, things are changing, Professor Snape has finally taken the position of Defence Against the Dark Arts Master and in his place a new Potions Master has been appointed, the avuncular Professor Slughorn, who has some secrets of his own.
 
There are questions to be answered too: what is the secret mission Dumbledore has in store for Harry? What is the mystery behind his newly blackened, shrivelled hand? What unspeakable pact has Draco Malfoy made?
 
There is deep magic at work here, dark magic, the magic of Horcruxes and bloody curses. Only the utmost bravery (and a pinch of liquid luck) will reveal the truth. For as the storm-clouds gather and suspicions grow around a traitor at the heart of Hogwarts itself, Harry and his friends are faced with the most bitter of betrayals.
 
The time for lessons is ending, the second war is beginning.