The Einstein Enigma by José Rodrigues dos Santos,

A Fórmula de Deus (God's Formula), in English The Einstein Enigma, is the fourth novel written by the Portuguese journalist and writer José Rodrigues dos Santos, published in 2006 in Portugal. It was the best-selling novel in Portugal in 2006, selling 100,000 copies.^[1]

The novel narrates a quest for the scientific proof of the existence of god by a Portuguese professor, Tomás Noronha, based on a formula developed by Einstein himself. The adventure takes place in Iran, Tibet and Portugal, with the involvement of the CIA. The book presents an innovative view about the origins of the universe, based on recent physics theories.

https://en.wikipedia.org/wiki/A_Fórmula_de_Deus
That book deals with the scientific proof of God existence and it is based on recent physics theory. God is not an exclusively religious issue, it is scientific as well. Who is God ? He is not a supernatural entity, he is natural as well. Nature around us is intelligent but to proove God's existence there must be an intention as well.  without intention life is just accidental and has no meaning. Anyway God’s intention is subtle and difficult to see. The author gives the example of a clock you come across with. Straight away you guess that there is an intelligence with a purpose who has made that clock. What about a flower, nature, people ?
Believe me or not I couldn't take my eyes off the book for hours on end.