Paths Not Taken — Simon R. Green

I'm John Taylor. I was born in the Nightside, that square mile in the hidden center of London where it is always the hour of the wolf, where gods and monsters walk side by side and where every dark question ever asked can be answered -- for a price.
           
I left for a while, but I did come back, to make my living doing what I do better than anyone else: finding things -- lost or stolen, real or imaginary.
           
Recently, I found the most dangerous thing of all: the true identity of my long-gone mother. Turns out she's a being who's been around since before the dawn of history. Then, she created the Nightside -- and now, for her own warped reasons, she intends to destroy it.
           
To stop her before she even gets started, I've got to do some hard traveling -- back in Time, through endless eons, into the very distant -- and probably deadly -- past…