"Right then," said the Ravenclaw hurriedly, "Accio wands." Three wands flew to her. She laughed shakily and handed her accomplice's wand back. "You brought the strips, right?"
"Of course, Cassie," responded the other girl. She rummaged in her knapsack and pulled out a small box. She withdrew two strips of what appeared to be white paper with a small orange square on the end. She passed one to the Ravenclaw and they hurried forward to touch a square to Harry and Ron's tongues. They retreated to the other side of the room and appeared to be comparing the strips to the box.
"They're clear," declared the Slytherin.
"Wait," called the Ravenclaw. "Shreya, there are too many variables. We never tested the effects of the silencing charm and the full body bind on pH."
"Well, what do you suggest? Wait until we experiment and then come back and try again? We have to do it now." She turned to the boys. "If we unhex you and give you all of the wands, you have to listen to us. Do we have a deal?" There was no response. "Oh bloody hell!" she exclaimed. She walked over to Ron, put her wand to his throat, and removed the bind. "Nod if we have a deal." Ron must have nodded for the girl unhexed him completely and dropped the wands.
Ron stood up, working the kinks out of his neck. He freed Harry, and then turned. "You haven't given us your wand, Ravenclaw," he spat. She dropped it and Harry moved to pick it up, but Ron had already pounced on it. He brandished his own wand at the girls, flushing with anger. "You two will pay for what you've done to Hermione!"
"Wait," called the Ravenclaw, "we're Hermione's friends and we can prove it!"
"You are?"
"You are?"
"We can?"
"We know the three of you used Polyjuice Potion in your second year to interrogate Draco Malfoy. You brewed it in Moaning Myrtle's bathroom using the recipe in Moste Potente Potions. Because of the research Hermione did with us, we know that neither of you is under the influence of Polyjuice Potion."
Harry lowered his wand. "Why did you think we might be using Polyjuice Potion?"
"Well, let's see," cut in the Slytherin, "you attacked me on the train with no provocation and, when I asked a simple question, you tried to duel me in the Great Hall. What on earth could have suggested you were behaving like Death Eaters-in-training?"
"Hold it," said Ron. How can you accuse us of acting like Death Eaters when you break into our common room, knock us out, and poke at our tongues."
"All right, lets not get bogged down in 'who acted like more of a Death Eater than whom.' That was a Polyjuice tester; we weren't poking your tongues for the heck of it. We invented them with Hermione," the Ravenclaw finished proudly then glanced at Ron with worry.
"Look," she said bluntly, "I went to muggle grammar school. I don't know if you did or how much chemistry you know."
Ron looked blank, but Harry spoke up, "I went to muggle grammar school. We did some science."
"Oh good, do you know what pH is?" she continued.
"Not really," he admitted.
"Acids and bases ring any bells?" the Slytherin asked.
"Yeah. Acids are things that burn, like lemon juice. Soap's a base, I think."
"That's right," the Ravenclaw continued, "The pH strips test if a substance is an acid or a base. An acid turns it red and a base turns it blue. Hermione told us about how badly the Polyjuice burns on the way down. We mixed up a small test batch and found it was a..."
"Acid!" Ron said triumphantly.
"No, a base. Anyway, we found that Polyjuice causes the drinker's mouth to tend toward the basic. We made the pH strips more sensitive, and we had our test."
"So," said the Slytherin, "now that we have the suspicions and threats out of the way, let's move on to the introductions. We know your names, of course. I am Shreya Sahni of Slytherin, and my Ravenclaw friend is Cassandra Ada Brenner who goes by Cassie or Cass as she sees fit. It is now close to midnight and we don't have time for chitchat. Meet us outside the Ravenclaw Common room after dinner tomorrow and we'll talk."
"Why Ravenclaw?" Ron asked suspiciously.
"Well," replied Cassie, "given the likely reaction of your dorm mates to a Slytherin in your midst, Gryffindor is out. Ditto Slytherin. I don't think either of you knows the pass into Hufflepuff, so Ravenclaw is the spot."
"We could sneak into Hufflepuff the same way you snuck into Gryffindor," retorted Harry pointedly.
"There's a problem with that plan, too," replied Shreya. "It is true that Hufflepuffs are a foolishly trusting as Gryffindors, so we wouldn't have trouble getting a first year to tell us the password. You two are hardly inconspicuous, however. We'll meet in Ravenclaw. Meet us at the statue of Uric the Oddball and we'll take you to our common room."
"All right," said Ron reluctantly. "Here are your wands back." He held them out like a two-pronged olive branch. Cassandra took hers back, but Shreya pulled another wand out of a pocket.
"I'm not dumb enough to hand over my real wand. Give that a wave; it turns into a dead parrot."
"A dead parrot?" Ron repeated, looking liable to snap the pseudo-wand and follow it up with the Slytherin's arm.
"Not just any dead parrot," she clarified, looking smug, "a Norwegian Blue. They have lovely plumage, I'm told. I bought it at Weasleys' Wizard Wheezes. We'll see you at the Ravenclaw common room tomorrow."
"What's the password?" asked Harry.
The two girls exchanged a look. "It's too complicated," Cassie said reluctantly. "We'll see you tomorrow." With that, the girls picked up their cloaks and walked out, leaving Harry with a baffled Ron.
"Well," Ron spluttered, "that's the strangest password I've ever heard in my life."