a culture based, and obsessed on the power of numbers. number's make a power.
it's about a written prophecy that was destroyed because it was so contreversial, it went totally against a countries religious belief. but destroying a prophecy doesn't make it not come true.
this culture has a...fear of the number 3. to them 3 represents evil. and their culture is centered around preventing the evil 3.
the holiest of numbers is 4. because 4 is one more than 3, and there's an ancient story about the 4 gods suppressing the 3 evils (it's a powerful evil).
ANYWAY: families can't have 3....3 children, nor can there be 3 of them per family. so Mom and Dad marry. Two is okay. When they have their First Child they invite one of their parents to live with them, to make it a group of 4 to negate the evil.
That is until they have their next child, then mom can return back home (or stay if she wants).
However the 3rd child born, though it makes a total of 5, is considered to be evil (it is their third child) so they have to kill it, or send it off away and totally deny that they had that child.
NOW another interesting thing is that if you deal in a shady business, or a dark art, and you go to practice it in public you HAVE to be in a group of 3. if you're caught committing a crime and don't have a 3rd person, it instantly means death. (because it is a form of deception), so the practice of "The Hidden Third" emerges, where a person is planted in a crowd, sitting alone, and if their group is caught they come forward and reveal themselves. This is acceptable, except the punishment for being caught (and in a 3rd) is a severe beating and a tell-tale mark placed upon the face (a large triangle scar on the face, the position is up to the marker).
However sometimes the 2 thieves committing the crime don't plan for a 3rd and then they just claim someone off the street, a beggar, a vagabond, etc. etc., and the "Surprise Third" has to play along, or face the removal of 4 fingers (two from each hand), while the other two are killed.
anyway, that's it.