No matter what you think of Dan Brown and his The Da Vinci Code, you must admit he was successful, and that he started something. He spawned a new genre. I don't know if you can call it the conspiracy theory genre, because that could encompass other things like international and local politics, or globalism and trade, diplomacy, war and terrorism. You can't really call it a plain thriller either, because plain thrillers rarely have the whole world looking stuff up to see if it was 'true'. Dan Brown invented the 'sailing close to perceived truths' genre. Or you could call it the 'send your reader on a quest' genre.
A number of other books of that kind came on the market since The Da Vinci Code had its unprecedented success, and many others written before The Da Vinci Code were re-read or discovered by newcomers to the genre.
If you google "books like the Da Vinci Code" you will get lists of similar books that feature quests, codes, biblical tie-ins, the art world, conspiracies, fast moving action, religion, historical content, scientific details, and mention of one or more household names within a mystery. These books also send their readers on a quest, looking up the information they find, to check its authenticity.
Readers feel that, if they find that there IS a pyramid at the Louvres
Museum, and that if there really IS a Roslyn Chapel in Scotland, then
the rest of the book must contain a grain of truth too.
They flock to buy the books, and they also buy others that 'explain' them.
If you like According to Luke, you might also enjoy:
The Flanders Panel by Arturo Peres-Reverte
An Instance of the Fingerpost by Iain Pears
Daughter of God by Lewis Perdue
The Kill Artist by Daniel Silva
The Splintered Icon by Bill Napier
Ex Libris by Ross King
The Rule of Four by Ian Caldwell & Dustin Thomason
The Genesis Code by John Case
The Gospel of Judas by Simon Mawer
The Confessor by Daniel Silva
The Prophetess by Barbara Wood
The Sign by Raymond Khoury
The Genesis Secret by Tom Knox
The Last Testament by Sam Bourne