The next day, Friday, Harry was overjoyed to finally be able to walk to class with Hermione again. Ron came with them, too. Potions sucked as usual, but Care of Magical Creatures looked interesting. There were a few brilliantly white horses nearby with horns on their heads…

"Ooh, look, unicorns," said Hermione, pointing.

The three of them walked to the paddock, where Sirius was standing, although he was a relatively far distance away from the unicorns.

"Good afternoon, class." Sirius smiled. "As you can see, today we will be studying unicorns. Girls, you can go up and pet them, but the boys should stay back. Unicorns prefer female company."

Hermione went to pet the unicorns with the rest of the girls; Sirius walked among them, handing out sugar cubes and apples. Harry and Ron were watching with interest, but their interest switched somewhere else as a familiar, well-endowed seventh year walked by, surrounded by some of her friends.

"There goes Holly," said Harry, nudging Ron. "The one who, um, helped Sirius with the tourniquet."

"I bet her…her you-know-whats are like soft pillows," said Ron dreamily.

"Smooth skin, too," Harry added.

"Oooooh," they said at the same time.

"I noticed Sirius wasn't staring at her when she was braless, though," Ron said thoughtfully.

"Well, first of all," said a voice from behind them, "she's my student."

They turned. There was Sirius, his arms crossed, one eyebrow arched slightly.

"Second," he continued, as both of them turned red, "she's about fifteen years younger than I am. And third, I already know what breasts look like."

Harry and Ron looked at each other, impressed.

"You do?" said Harry.

"Of course," Sirius replied. "What did you two think girls have got in their bras? Water balloons?"

They both shrugged. It was a great mystery.

"What happens when you squeeze 'em?" Ron asked eagerly.

"All right, that's enough," said Sirius. "Get back to the paddock, go on, we're going to take some notes."

…

Quidditch season was in full swing now. Hermione assured Harry that she would come to every one of his matches, and the two of them had promised to never fight again. Harry got the feeling that she, like him, felt that the troll incident had bonded them. Hermione also borrowed a book from the library, Quidditch Through the Ages, and lent it to Harry, because his first Quidditch match ever was coming up soon.

The day before the match, Harry, Ron and Hermione were outside in the cold courtyard, enjoying a warm fire Hermione had conjured up for them, when Sirius ran up to them excitedly.

"Look, another letter from Barbara!" he panted.

"How does she get letters to you?" Harry asked. "I doubt she uses an owl."

"I gave her the address to the Hogsmeade P.O. box," Sirius explained. "Whenever she wants to send me a letter, she just addresses it to there. The Muggle mailman takes the letter from her, and he delivers it all the way to the nearest Muggle post office."

"How does the letter get all the way to Hogsmeade, then?" said Ron.

"There's a wizard who works there in secret," Sirius explained, "and when he's going through the mail, he picks out the letters addressed to witches and wizards in the area, and takes them to Hogsmeade. Then, you just go to the post office and check the Muggle mailbox there."

"It's quite clever, really," said Hermione.

"Let's read it!" Sirius eagerly opened the letter and was just about to read when Snape approached them. For some reason, he was limping.

"What's that?" Snape demanded.

"It's a letter, duh," said Sirius.

"Not that." Snape pointed at Harry's borrowed library book. "That."

"Just a library book," Harry said innocently, showing it to him.

"Library books are not to be taken outside the school," Snape snapped. "Five points from Gryffindor."

"You made that rule up!" Sirius shouted. "Give him back those five points!"

"Be quiet, Professor Black," Snape told him. "Everyone knows you favor Gryffindor."

"Oh, and you totally don't favor Slytherin," Sirius said back. "Well, WE'RE going to win the House Cup this year!"

"Who's 'we'?" said Snape smoothly. "Aren't you not supposed to take sides, as a teacher?"

"Kind of the pot calling the kettle black, aren't we, Snape?"

"Now, now, you two, please stop fighting," said Hermione reasonably. "Fighting never solves anything."

Snape turned on his heel, taking the book with him. Sirius sighed.

…

That night, Harry wanted his book back. So he went down to the staffroom, hoping maybe Snape had left it in there. Snape might not be too willing to surrender the book, but maybe if there were other teachers there, he wouldn't argue. But when Harry knocked on the door, there was no answer.

Harry opened the door.

Snape was there with Filch, just the two of them. Snape was holding up his robes and Filch was handing him bandages. Snape's leg was a bloody, mangled mess, not unlike Wormtail's arm before Madam Pomfrey had fixed him.

"Blasted thing," Snape said. "How are you supposed to keep your eyes on all three heads at once?"

Just as Harry was trying to leave without being noticed, Snape caught his eye.

"POTTER!" he hollered, dropping his robes.

"I was wondering if I could have my book back," Harry told him nervously.

"GET OUT! OUT!"

Harry ran all the way back up to Gryffindor Tower, where Ron and Hermione were waiting for him, and he told them about his Snape encounter.

"You know what this means?" he said. "He tried to get past that three-headed dog at Halloween! He's after whatever it's guarding! And I'd bet my broomstick he let that troll in, to make a diversion!"

"No—he wouldn't," Hermione insisted. "I know he's not very nice, but he wouldn't try and steal something Dumbledore was keeping safe."

"Honestly, Hermione, you think all teachers are saints or something," said Ron. "I'm with Harry. I wouldn't put anything past Snape. But what's he after? What's that dog guarding?"

"Do you think we could ask Sirius?" said Hermione, turning to Harry.

"I don't think even he knows," Harry told her. "It might just be Dumbledore and the gamekeeper, Hagrid. When Sirius and I were in Diagon Alley, we ran into him when he was retrieving whatever it is. It was so top-secret, they had to just say 'You-Know-What'."

….

"He didn't catch it, he nearly swallowed it!"

The match had been lost…that is, for Slytherin. Gryffindor had won by 170 points to 60. But Harry wasn't focusing on the victory; he was focusing on something that had happened during the match, as were Ron, Hermione and Sirius, who were hauling him off to Sirius's teacher's quarters.

"What happened?" Sirius asked, looking worried. "You lost control of your broomstick?"

"Yeah," said Harry shakily. "I don't know why, though."

"Snape did it," Ron told them.

"It was Snape?" Sirius repeated. "You think he was jinxing the broom?"

"Yeah," said Ron. "I saw him. So did Hermione."

"Oh God, a jinx…" Sirius frowned. "But he would have had to keep eye contact with Harry all through the game. You have to keep eye contact when you jinx something, you know."

"Of course I know," said Hermione, "and he didn't take his eyes off Harry until I used one of my portable fires on him!"

"I wouldn't have believed it." Sirius let his breath out through his nose. "I mean, Snape is a nasty person, but even he wouldn't try to kill a student, would he?"

"Listen, Sirius…" Harry swallowed. "Do you remember that troll from Halloween night?"

"No," said Sirius sarcastically; then, "of course I remember, it almost killed you and Hermione, didn't it?"

"Yeah, well, we know why there's a Forbidden Corridor," Ron told him. "It's because there's a giant three-headed dog there, guarding something—no joke. It's right over a trapdoor. And we think Snape let the troll in, as a diversion, so he could get to whatever the dog is guarding. We think he wants to steal it."

"How do you know?" Sirius asked anxiously.

"I think the dog bite on his leg told me well enough," Harry said flatly. "It looked like the one you gave Wormtail."

There was a long pause, then finally Sirius spoke.

"That settles it," he said.

"It settles what?" Harry asked.

"Our classes, remember?" Sirius stood up. "Quirrell can't teach you Defense Against the Dark Arts. You need a real teacher. We're going to start as soon as possible."