Harry Potter: The Order of the Phoenix & The Half-Blood Prince

Explanation: Dolores Umbridge, High Inquisitor and the most hated character in the saga. Dressed in pastel pink, surrounded by kitten plates, she gives students detentions with a quill that carves into their flesh.

Explanation: Dumbledore's Army (D.A.), meeting secretly in the Room of Requirement. Members sign a parchment cursed by Hermione: Marietta Edgecombe, who betrays them, ends up with "SNEAK" spelled out in pimples across her face.

Explanation: 12 Grimmauld Place in London, the ancestral home of the Black family. Sirius inherits the house and lets the Order use it. It's Unplottable (protected by the Fidelius Charm) with Dumbledore as Secret-Keeper.

Explanation: The Department of Mysteries, which studies time, space, death, love, thought, and prophecies. The battle pits the D.A. against Death Eaters around the prophecy orb containing the prediction about Harry and Voldemort.

Explanation: Bellatrix Lestrange, his own cousin, they are both Blacks. Sirius falls through the Veil, a magical archway to the afterlife from which no one returns. His death plunges Harry into deep rage.

Explanation: An otter. Every Patronus reflects the wizard's personality. Hermione learns to conjure a corporeal Patronus alongside Harry during the secret Dumbledore's Army meetings in the Room of Requirement.

Explanation: Occlumency. Snape teaches this discipline to Harry in Book 5 so Voldemort can no longer manipulate him, unsuccessfully, Harry never really masters it. The opposite art is Legilimency (reading minds).

Explanation: Cho Chang, a Ravenclaw student one year older, Cedric Diggory's former girlfriend. Their kiss under the mistletoe in the Room of Requirement goes badly because she is still grieving Cedric. Their relationship doesn't last.

Explanation: Severus Snape. His mother Eileen Prince was a pure-blood witch, his father Tobias Snape a Muggle, hence "Half-Blood". Snape had annotated his old potions textbook with improvements and even invented spells like Sectumsempra.

Explanation: Felix Felicis. A single vial gives 12 hours of total luck. Harry shares it with Ron and Hermione in Book 6. He notably uses it to extract from Slughorn a crucial memory about Horcruxes.

Explanation: Amortentia, the most powerful love potion in the world. For Hermione, it smells of parchment, freshly-mown grass, and Ron's hair. The scent reveals attraction, no potion can create true love.

Explanation: Sectumsempra. The spell creates wounds like slashes from an invisible sword. Snape arrives in time to save Draco by chanting a counter-spell, and Harry realises the true nature of the "Prince". He hides the book in the Room of Requirement.

Explanation: Draco Malfoy. Voldemort assigns him this mission to punish his father Lucius's failure at the Department of Mysteries. Draco prepares his plan all year through the Vanishing Cabinet from Borgin and Burkes, but can't bring himself to kill Dumbledore.

Explanation: "I must not tell lies", Umbridge's message is carved into Harry's flesh in Book 5, over hours of detention, because he dares to say Voldemort is back. The scar remains visible for the rest of his life.

Explanation: Firenze, a centaur from the Forbidden Forest, hired by Dumbledore after Trelawney is sacked by Umbridge. His herd banishes him for serving humans. He teaches in a classroom magically transformed into an enchanted forest glade.