Q:

A genre about hidden/secret history of the world

I am looking for a genre that I cannot really find to have a common name, but what can be described as a secret or hidden history of the world. 
Much like Lovecraft where his heroes were studying ancient manuscripts to uncover the ancient and forgotten knowledge. Where the ancient people knew things that were discovered long after that can only be explained by some facts unknown to modern science.
I tried to google, but could not find anything interesting. Since it's not really allowed to ask about the authors themselves I would appreciate any hints that can help me google this. A common name for the genre, or some other least common denominator that I can use to search e.g.
P.S. Not looking for "documentary" conspiracy theories, but pure fiction.

A:

There are two such genres, really. The first is well-known, that would be the "spy thriller", sometimes put down as "espionage". Not all spy thrillers contain "secret histories", only a (not small) subset do. Everything's classified, only a few people ever really know the truth of what happened.
The other genre I do not know a good label for, but it tends to not involve spies or intelligence agencies. Private individuals are the main protagonists and antagonists. If government agencies are involved, it's only temporarily or tangentially so (television: Supernatural, The Librarians). The secrets are often of a supernatural/fantasy/science fiction nature.
Sometimes both are combined (Hellboy movies, Charles Stross's stuff). 
I propose that the latter genre/category be called "covert fantasy". We could tag it as such, and without even checking I know that there will be several other questions that would use it.

