Fidelius Charm

From UnknowableWiki

The Fidelius Charm is a spell that enables secret information to be hidden within the soul of a chosen recipient, known as the Secret-Keeper. The information is then irretrievable until the Secret-Keeper chooses to reveal it; even those who have had this information revealed to them cannot tell it to others (PA10).

The Fidelius Charm does not seem to work against elf magic. At Harry Potter's request, Dobby is able transport himself and others to Shell Cottage despite the Fidelius Charm that Bill Weasley has set on the place (DH23, DH24).

One or more of many protective enchantments cast on Shell Cottage prevent wizards from Apparating or Disapparating; it is mentioned that the Fidelius Charm is responsible for this (DH24), but such a property would be incoherent with the fact that, a few months before this, Hermione Granger Apparates with Yaxley into the boundaries of the protection of the Fidelius (DH13, DH14).

Revealing the secret

In addition to the obvious spoken word, there are other ways to reveal the object or person protected by the Fidelius Charm:

Alastor Moody uses a handwritten note from Albus Dumbledore to reveal the secret of the Order of the Phoenix headquarters to Harry Potter (OP3).
Hermione Granger accidentally reveals the secret of the location of number twelve, Grimmauld Place to Yaxley when he Side-Along-Apparates with her to the house (DH13, DH14).
Dobby's transportation of Harry, Ron, Hermione, Dean, Luna, Griphook and Ollivander to Shell Cottage seems to have revealed the secret to them automatically (DH24); however, this may also have happened when Bill, the Secret-Keeper, ran out of the house to meet them.
The house that Lily and James Potter inhabited in Godric's Hollow at the time of their death is visible to wizards, with a sign that marks its significance. This in all likelihood means that when the subjects of the Fidelius Charm die, the secrecy does so as well (DH17).

Death of the Secret-Keeper

In her website, J. K. Rowling explained that, when the Secret-Keeper dies, the secret remains as it was at the time of his or her death; only the people to whom the Keeper revealed the secret know it, and they are unable to tell anyone else (JKRW). However, Rowling seems to have changed her mind by the time she wrote Harry Potter and the Deathly Hallows.

In the summer of 1997, Arthur Weasley explains that Albus Dumbledore's death caused the secret of the Order of the Phoenix headquarters at number twelve, Grimmauld Place to change Secret-Keepers: everyone to whom Dumbledore had revealed the secret became Seeker-Keeper in his stead. Alastor Moody sets in place a few hexes at number twelve, including a Tongue-Tying Curse, hoping to prevent Severus Snape from sharing the secret with Lord Voldemort. Nevertheless, the high number of Secret-Keepers dilutes the power of the Fidelius Charm, for this gives Voldemort nearly twenty different people whom he can attack to coerce them into revealing the secret. For this reason, Order members prefer to use The Burrow as headquarters (DH6).

Uses in the series

When Harry Potter was an infant, his parents hid and protected themselves from Lord Voldemort with the use of this charm. They had selected Sirius Black to be Secret-Keeper. Black, however, suggested that they use the inconspicuous Peter Pettigrew instead, claiming that it would be a perfect and unexpected ruse. Unbeknownst to them, Pettigrew was a Death Eater, and betrayed the Potters' trust, revealing their whereabouts to Voldemort. Lily and James were murdered on October 31, 1981. Peter later framed Black for the crime; Sirius was sent to Azkaban and spent 12 years therein (PA18).
This charm is used to hide the location of the Headquarters for the Order of the Phoenix at number twelve, Grimmauld Place. Albus Dumbledore is the Secret-Keeper, and reveals the information to the other members of the Order (OP6). After his death, as stated above, all Order members become Secret-Keepers, and they choose to use The Burrow as headquarters for fear of Lord Voldemort finding out about Grimmauld Place (DH6).
In 1998, Muriel's house is protected by the Fidelius Charm so that the Weasleys can hide there; Arthur Weasley is the Secret-Keeper.
Bill and Fleur Weasley's house, Shell Cottage, is also protected by the spell, and Bill is the Secret-Keeper (DH24).