In case you hadn't notice the big "Book One" or the number 1 on the spine of the book, here's a newsflash: this is the first book in a series. A looong series. The end of this book is just setting you up for the next one.
Which is probably why it leaves Amy and Dan at a disadvantage. They've unwillingly given up the glowing vial to the Kabra siblings, but they know where they're headed next: Vienna, to follow a trail of clues having to do with Wolfgang Amadeus Mozart.
It's the kind of cliffhanger ending that makes sure we desperate readers will be clamoring for the next book, as soon as we flip the last page of this one. So what are you waiting for? Get out there and get Book Two.