Although Bill was already in his fifth year and an excellent student, school rules stated that students were not allowed into the Restricted Section without a note signed by a professor.
There had been no such rule before. It was mainly because Voldemort had visited the Restricted Section after coming to the school, found some information there, and subsequently developed questions he asked Slughorn about.
But as Flitwick's prized student, Bill could easily obtain a note bearing Flitwick's signature. He could move freely through the Restricted Section like a professor.
One day, he encountered Carter in the Restricted Section. It should not have been strange; there was no rule saying a professor skilled at Quidditch could not read.
Yet Bill followed him and discovered that Carter had not handed the book to Madam Pince. Instead, he found an empty spot, copied it, took the duplicate away, and left the original in the library.
Naturally, this was because he and Madam Pince had fallen out over some matter.
After Carter left, Bill picked up the book Carter had borrowed and leafed through it.
Besides Goblin enchanted iron and magic silver, there was another substance resembling gold. Even among Goblins, it was only a legend.
Its status was similar to the Philosopher's Stone. The Philosopher's Stone turned base metals into gold, but this kind of gold could not be created by the Philosopher's Stone.
"So if he finds it, Carter won't have to hand the Sword of Gryffindor over to the Goblins?" Pomona asked.
"Who told you he planned to give the Sword of Gryffindor to the Goblins?" Severus countered.
Pomona was momentarily speechless.
"He believes it is at Hogwarts, and that Barnaby knows where it is," he continued.
"How could Barnaby know about that?" Pomona asked.
"Because of Paul." Severus pressed