And it's not being held at Gringotts!
In an exclusive interview, the people who will publish the fifth Potter book in the UK - Bloomsbury - told us security surrounding the manuscript was very tight.
It is also still being edited by Emma Matthewson, who worked on the last three books in the series.
Emma is one of the only two people lucky enough to have the read the story so far.
The other is Bloomsbury chief executive Nigel Newton. They share an office in Soho Square, west London.
But the manuscript is not there! So where in the world can it be?
Well, as soon as we know, we'll tell you!
Work on the artwork for the book's cover is also expected to begin very soon.
Then the design will be revealed on Bloomsbury's website.
At 768 pages, the new book will be much longer than The Goblet of Fire, which Bloomsbury say is "fantastic".
So don't forget to keep checking our site for the latest news on everything you need to know about Harry Potter.