2 Peter 1:20-2:3 says:
...knowing this first, that no prophecy of Scripture is of any private interpretation, 21 for prophecy never came by the will of man, but holy men of God spoke as they were moved by the Holy Spirit.
2 But there were also false prophets among the people, even as there will be false teachers among you, who will secretly bring in destructive heresies, even denying the Lord who bought them, and bring on themselves swift destruction. 2 And many will follow their destructive ways, because of whom the way of truth will be blasphemed. 3 By covetousness they will exploit you with deceptive words; for a long time their judgment has not been idle, and their destruction does not slumber.
Thus be careful. Dan Brown's works in particular have been easily disproved, because what he writes is (I'm hoping meant to be) well-woven fiction, not serious theology. Unfortunately, in order to maintain the illusion, he chooses not to make this distinction clear. Not many writers do, for instance, does JK Rowling preface Harry Potter by noting that what you are about to read is make-believe? Dan Brown may well be foolish not to, though since he works from a sacrad text.
One of the rules of Bible interpretation is that scripture cannot mean anything now that it didn't mean when it was written. There are prophecies that aren't obvious at surface level, but they CANNOT be interpreted without revelation from God. If you want to understand how this works, study how the Old Testament prophecies about Jesus are revealed in the New Testament via Jesus or the Holy Spirit. Note too how most of these prophecies could not be deciphered before Jesus came (which would have interfered with his coming), but their existence was useful for showing that Jesus was the prophesied Christ. Thus you should also ask what the purpose of a supposed hidden meaning is. If the only effect is to provide a sense of superiority that you have hidden knowledge, than you can pretty much be sure that the meaning is false, and not of God who values humility.