's Snape got to do with it？〃
〃He's here； Sirius；〃 said Lupin heavily。 〃He's teaching here as well。〃 He looked up at Harry； Ron； and Hermione。
〃Professor Snape was at school with us。 He fought very hard against my appointment to the Defense Against the Dark Arts job。 He has been telling Dumbledore A year that I am not to be trusted。 He has his reasons。。。 you see； Sirius here played a trick on him which nearly killed him； a trick which involved me 〃
Black made a derisive noise。
〃It served him right；〃 he sneered。 〃Sneaking around； trying to find out what we were up to。。。 hoping he could get us expelled。。。。〃
〃Severus was very interested in where I went every month。〃 Lupin told Harry； Ron； and Hermione。 〃We were in the same year； you know； and we er didn't like each other very much。 He especially disliked James。 Jealous； I think； of James's talent on the Quidditch field。。。 anyway Snape had seen me crossing the grounds with Madam Pomfrey one evening as she led me toward the Whomping Willow to transform。 Sirius thought it would be er amusing； to tell Snape all he had to do was prod the knot on the tree trunk with a long stick； and he'd be able to get in after me。 Well； of course； Snape tried it if he'd got as far as this house； he'd have met a fully grown werewolf but your father； who'd heard what Sirius had done； went after Snape and pulled him back； at great risk to his life。。。 Snape glimpsed me； though； at the end of the tunnel。 He was forbidden by Dumbledore to tell anybody； but from that time on he knew what I was。。。。〃
〃So that's why Snape doesn't like you；〃 said Harry slowly； 〃because he thought you were in on the joke？〃
〃That's right；〃 sneered a cold voice from the wall behind Lupin。
Severus Snape was pulling off the Invisibility Cloak； his wand pointing； directly at Lupin。
CHAPTER NINETEEN
THE SERVANT OF LORD VOLDEMORT
Hermione screamed。 Black leapt to his feet。 Harry felt as though he'd received a huge electric shock。
〃I found this at the base of the Whomping Willow；〃 said Snape； throwing the cloak aside； careful to keep this wand pointing directly at Lupin's chest。 〃Very useful； Potter； I thank you。。。。〃
Snape was slightly breathless； but his face was full of suppressed triumph。 〃You're wondering； perhaps； how I knew you were here？〃 he said； his eyes glittering。 〃I've just been to your office； Lupin。 You forgot to take your potion tonight； so I took a gobletful along。 And very lucky I did。。。 lucky for me； I mean。 Lying on your desk was a certain map。 One glance at it told me all I needed to know。 I saw you running along this passageway and out of sight。〃
〃Severus 〃 Lupin began； but Snape overrode him。
〃I've told the headmaster again and again that you're helping your old friend Black into the castle； Lupin； and here's the proof。 Not even I dreamed you would have the nerve to use this old place as your hideout 〃
〃Severus； you're making a mistake；〃 said Lupin urgently。 〃You haven't heard everything I can explain Sirius is not here to kill Harry 〃
〃Two more for Azkaban tonight；〃 said Snape； his eyes now gleaming fanatically。 〃I shall be interested to see how Dumbledore takes this。。。。 He was quite convinced you were harmless； you know； Lupin。。。 a tame werewolf 〃
〃You fool；〃 said Lupin softly。 〃Is a schoolboy grudge worth putting an innocent man back inside Azkaban？〃
BANG！ Thin； snakelike cords burst from the end of Snape's wand and twisted themselves around Lupin's mouth； wrists； and ankles； he overbalanced and fell to the floor； unable to move。 With a roar of rage； Black started toward Snape； but Snape pointed his wand straight between Black's eyes。
〃Give me a reason；〃 he whispered。 〃Give me a reason to do it； and I swear I will。〃
Black stopped dead。 It would have been impossible to say which face showed more hatred。
Harry stood there； paralyzed； not knowing what to do or whom to believe。 He glanced around at Ron and Hermione。 Ron looked just as confused as he did； still fighting to keep hold on the struggling Scabbers。 Hermione； however； took an uncertain step toward Snape and said； in a very breathless voice； 〃Professor Snape it it wouldn't hurt to hear what they've got to say； w would it？〃
〃Miss Granger； you are already facing suspension from this school；〃 Snape spat。 〃You； Potter； and Weasley are out…of…bounds； in the pany of a convicted murderer and a werewolf。 For once in your life； hold your tongue。〃
〃But if if there was a mistake 〃
〃KEEP QUIET； YOU STUPID GIRL！〃 Snape shouted； looking suddenly quite deranged。 〃DON'T TALK ABOUT WHAT YOU DON'T UNDERSTAND！〃 A few sparks shot out of the end of his wand； which was still pointed at Black's face。 Hermione fell silent。
〃Vengeance is very sweet；〃 Snape breathed at Black。 〃How I hoped I would be the one to catch you。。。。〃
〃The joke's on you again； Severus；〃 Black snarled。 〃As long as this boy brings his rat up to the castle〃 he jerked his head at Ron 〃I'll e quietly。。。。〃
〃Up to the castle？〃 said Snape silkily。 〃I don't think we need to go that far。 All I have to do is call the dementors once we get out of the Willow。 They'll be very pleased to see you； Black。。。 pleased enough to give you a little kiss； I daresay。。。 I 〃
What little color there was in Blacks face left it。
〃You …you've got to hear me out；〃 he croaked。 〃The rat look at the rat 〃
But there was a mad glint in Snape's eyes that Harry had never seen before。 He seemed beyond reason。
〃e on； all of you；〃 he said。 He clicked his fingers； and the ends of the cords that bound Lupin flew to his hands。 〃I'll drag the werewolf。 Perhaps the dementors will have a kiss for him too 〃
Before he knew what he was doing； Harry had crossed the room in three strides and blocked the door。
〃Get out of the way； Potter； you're in enough trouble already；〃 snarled Snape。 〃If I hadn't been here to save your skin 〃
〃Professor Lupin could have killed me about a hundred times this year；〃 Harry said。 〃I've been alone with him loads of times； having defense lessons against the dementors。 If he was helping Black； why didn't he just finish me off then？〃
〃Don't ask me to fathom the way a werewolf's mind works；〃 hissed Snape。 〃Get out of the way； Potter。〃
〃YOURE PATHETIC！〃 Harry yelled。 〃JUST BECAUSE THEY MADE A FOOL OF YOU AT SCHOOL YOU WON'T EVEN LISTEN 〃
〃SILENCE！ I WILL NOT BE SPOKEN TO LIKE THAT！〃 Snape shrieked； looking madder than ever。 〃Like father； like son； Potter！ I have just saved your neck； you should be thanking me on bended knee！ You would have been well served if he'd killed you！ You'd have died like your father； too arrogant to believe you might be mistaken in Black now get out of the way； or I will make you。 GET OUT OF THE WAY； POTTER！〃
Harry made up his mind in a split second。 Before Snape could take even one step toward him； he had raised his wand。
〃Expelliarmus！〃 he yelled except that his wasn't the only voice that shouted。 There was a blast that made the door rattle on its hinges； Snape was lifted off his feet and slammed into the wall； then slid down it to the floor； a trickle of blood oozing from under his hair。 He had been