Okay. Now my skin is really prickling. I've read all the Harry Potter books, all five of them. I don't remember any half-blood prince."What's this?" Trying to sound casual, I point at the ad, "What's Harry Potter and the Half-Blood Prince?""That's the latest book," Garth the other trainee, says. "It came out ages ago."I can't help gasping. "There's a sixth Harry Potter?""There's a seventh out soon!" Diana steps forward eagerly. "And guess what happens at the end of book six-""Shh!" exclaims Nicole, the other nurse. "Don't tell her!