|Nội dung||Protects a secret|
|Xuất hiện lần đầu||Harry Potter and the Prisoner of Azkaban|
The Fidelius charm is "an immensely complex spell" that conceals a secret within a living soul -- the "secret-keeper". It is coined from the Latin 'fides' -- faith. It is first described in detail in Harry Potter and the Prisoner of Azkaban, and is also mentioned in Harry Potter and the Order of the Phoenix and Harry Potter and the Deathly Hallows.
The Fidelius charm is a very powerful protection for information; having locked the secret into a soul, even direct inspection of the secret will not, apparently, reveal it. Professor Flitwick, in the description of the spell, says "As long as the Secret-Keeper refused to speak, You-Know-Who could search the village where Lily and James were staying for years and never find them, not even if he had his nose pressed against their sitting-room window!" (Lily and James Potter had gone into hiding at that point because they had information that Voldemort was specifically seeking them.) The conclusion reached at that time, correctly, is that the Secret-Keeper must have voluntarily divulged the secret to Voldemort.
The location of the headquarters of the Order of the Phoenix, also, is protected by the Fidelius charm; in this case, the Secret-Keeper is Albus Dumbledore. At this stage in the story, Dumbledore is not willing to talk directly to Harry, but he is able to convey the information about where the Order is located to Harry, by means of writing. Having shown him the note, Alastor Moody cautions him about reading it out loud or repeating it; one has to wonder why, because the Fidelius spell blocks anyone but the Secret-Keeper from revealing the secret... so presumably Harry would have been somehow blocked from speaking the contents of that note.
- What would have happened had Harry tried to read the note about the location of the Order out loud?
- What would happen if a secret keeper died before revealing the secret to anyone?
J. K. Rowling had implied that when a Secret-Keeper dies, the ability to divulge the secret dies with him. The Fidelius Charm prevents anyone except the secret-keeper from revealing the secret; the people to whom he releases the secret are privy to it, of course, but cannot tell anyone else. At the death of a Secret-Keeper, then, everyone who knew the secret would retain that knowledge; but, the implication was, as before they could not pass it on, so the secret would go no further.
If that were the case, it could prove difficult to move the headquarters of the Order after Dumbledore's death. The secret that Dumbledore is protecting is the location of the headquarters of the Order of the Phoenix; if the ability to pass on that secret died with the secret holder, it would not be possible to tell anyone, even holders of the current secret, where the new Headquarters were. If the Order were to disband, presumably that would make the secret moot and break the charm, but that is not likely to happen until some time after Voldemort's final defeat.
Additionally, it would cause some problems for Harry in book 7. It is his stated intention to visit his parents' house in the village of Godric's Hollow; but as the secret-keeper, Peter Pettigrew, is apparently still keeping the secret, it may prove difficult for him to find it. In fact, it did not seem to be too difficult for Rubeus Hagrid to find it immediately after the incident; while Sirius Black was also present at the time, he almost certainly had been told the secret by Pettigrew earlier.
There is a great deal of discussion on various fan sites about the "missing day"; Voldemort had been dead for a full day before Hagrid appeared at Privet Drive with Harry. It is believed by many fans that the occurrences during that day would be important, possibly even pivotal, to events in the seventh book. It is entirely possible that, if the Fidelius spell was still active, Hagrid would have been unable to find the place until one of the parties to the secret was there. We can safely assume that Sirius, as one of the Marauders, would have been aware of the Potters' location; in fact, he does say, in Harry Potter and the Prisoner of Azkaban, that he had seen "the bodies and the destruction" of the house, so he must have known the secret, either before the Fidelius charm was performed, or by Peter informing him of it afterwards. If the Fidelius charm was still active, Hagrid would have been unable to enter the remains of the house to recover Harry until Sirius appeared on the scene; and it would have been Sirius who actually removed Harry from the wreckage and passed him to Hagrid to carry back to Little Whinging. Against this, of course, is Hagrid's statement that he carried little Harry out of the wrecked house himself, which would strongly imply either that Hagrid had been informed of the secret, or that the Fidelius charm's effect ended with the deaths of the Potters.
It turns out, however, that the author's statement is at the very least misleading. Mad-Eye Moody explains that with the death of Dumbledore, everyone who had been party to the secret before is now a Secret-Keeper for the secret themselves. As a result, when Hermione accidentally Side-Along-Apparates Yaxley (a Death Eater) to the front step of Grimmauld Place, she assumes that she has revealed the secret to him.
The Fidelius spell is one of several that seem to have their effects altered at the whim of the author in the course of the story arc. Firstly, of course, there is the question of what happens to the secret when the Secret-Keeper dies; what was written on the author's web site, and what actually happened, were subtly different, as mentioned above. It seems the author changed the behavior, to make all secret-holders become secret keepers, as it seemed necessary in order to force Harry, Ron, and Hermione out of Grimmauld Place. Further, and again in the final book, Harry, with assistance from Dobby, escapes to Shell Cottage, a safe house that is protected, we are told, by the Fidelius charm. Yet Harry, despite not having been told its location by Bill Weasley, the secret-keeper, is able to see the cottage immediately upon arriving. Granted, we are told that Dobby is able to take people to Shell Cottage earlier, though it is unlikely he would have been granted access to that secret by Bill Weasley; it is possible that Dobby's House-elf magic would give Dobby the ability to bypass the Fidelius charm, but that would not extend to Harry, Hermione, Mr. Ollivander, Luna Lovegood, or Dean Thomas, all of whom accompany Harry and Ron to Shell Cottage on that occasion, and none of whom have had occasion to be let into the secret by Bill Weasley.