This is the headquarters of the [[Magical Organizations of Interest/The Order of the Phoenix]], which is the childhood home of [[Sirius Black]] (which he has inherited by the time the reader sees the house). It's unplottable, done by Sirius' dad so [[Muggle]]s cannot come to call, and [Dumbledore](Albus%20Dumbledore) puts the [[Fidelius Charm]] on it with him as secret keeper. This is the namesake of chapter [4 - Number Twelve, Grimmauld Place](4%20-%20Number%20Twelve,%20Grimmauld%20Place.md) in book [5 - Order of the Phoenix](Books/5%20-%20The%20Order%20of%20the%20Phoenix/The%20Order%20of%20the%20Phoenix.md).