That is our point of departure." "A somewhat vague one." "Let us see then if we can narrow it down.

As I focus my mind upon it, it seems rather less impenetrable.

What indications have we as to this book ?" "None." "Well, well, it is surely not quite so bad as that.

The cipher message begins with a large 534, does it not?
We may take it as a working hypothesis that 534 is the particular page to which the cipher refers.
So our book has already become a large book which is surely something gained.

What other indications have we as to the nature of this large book?
The next sign is C2.