This book sets out to explain a different path, for characters who want power but without becoming a standard delta. They are the bargainers, magic-users of the Brave New World if you like, doing their thing by making pacts, bargains, with spirits. Generally not very nice ones. The process starts pretty much like becoming a delta, surviving a near-death harrowing experience, only the character does not become a delta. They start hearing voices instead...
The first part of the book delivers in-character information in the form of a series of web pages, these ones written by a Mister Twist for beginning Bargainers explaining to them just what their new-found powers might be. Dealing with demons, basically. There's all manner of background material, the long history of how the demons came to be and how they interact with mere mortals, deltas though they might be. It creates a mythology all of its own, which may not sit too well with players who have religious beliefs - just sit back and remember that this is a game, or decide that you won't play a Bargainer or even have them in your game if you feel this is all too offensive to your faith. This cosmology posits a Heaven and a Hell, each with inhabitants, and it is the Demons from Hell that Bargainers associate with.
The first true bargainer, it's said, was Houdini. There's a fair bit of background on him, and then we get down to the nitty-gritty of how to make a deal with a demon and the basic ground rules that you should adhere to for your own safety and sanity. There's also plenty on bargainer society and support, the folks a new bargainer will associate with and learn from. The main means of communication for these quite solitary types is a mailing list and an annual convention.
Bargainers have enemies too, not just the government and Delta Prime, but the Covenant (representing Christian belief) and even devil-worshippers. They can cause quite a nuisance of themselves, even before they manage to make contact with a real demon... and then there's the Heavenly Host, the angels themselves. And other magic-users like shamans and practicioners of voodoo.
Eventually we emerge into game mechanics with a chapter Bargains and Bargainers, which takes all this in-character material and shows you how to make it work in game terms. There are six bargainer archetypes to use as is or as inspiration for your own character, and a wealth of other material as well. Bargainers gain access to some actual magic spells, you see, and these are laid out for you here.
The Guide's Handbook section follows, and as usual promises to reveal the truth of the matter. Along with that, it explains how to take the demon's part in a bargain and presents a host of appropriate adversaries.
Finally, the Author's Afterword explains how Brave New World is by no means a standard superhero game, and reveals a little about how his vision for it hangs together.
Are bargainers optional? They certainly do not need to play a large role, but if they are not there, somewhere in the background, your game will be the poorer for their absence.