The boy let out a "wow" and Trisha had to agree. It was rather amazing. When he took the book from her, she suddenly didn't know what to do with her hands, so she clasped them in front of her. He thanked her and she nodded. Just when Tris was about to turn back to look for a new book, he added something quietly and she turned back.
"I'm sure there's a spell that will show it. Don't you think?" She replied lightly. "Though, we're underage so it can't be either of us that casts it."
For a Ravenclaw, she was having trouble digesting what was going on. Things like invisible books, in the world she was from, shouldn't exist. Then again, she'd had five years to get used to the idea that her life was full of things that shouldn't exist or shouldn't happen. Just look at Quidditch. Even so, she wasn't really being much of a help to the boy right then.
"I'm sorry, I can't think of another way, unless you use the Muggle way of detection." Trisha said, referring to the old idea of lemon juice and heat being used to uncover invisible ink. Would it even work? "I have a bad feeling it might hurt the pages, though." Books, in her mind, were practically sacred and she wasn't going to be the one to hurt the book in question.