The fix was in from the get go. All that had to be determined was who was going to make the public announcement, if any.
Clinton assigned Comey to the task. He's a smoother talker. Lynch was told to stand down, and to stand down all of DOJ, that Comey was going to handle all the publicity. No promise needed to be offered, no quid pro quo. An simple order from the godfather would get the job done.
Setting aside reasonable speculation of what happened behind the scenes, the Hillary e-mail problem is still self-evident. It could not happen that the nominee would be charged, and it had to happen that the public be addressed on the subject. It had to happen because the status quo players demanded it, not because the system did.
Comey's book is just trying to sell the same old claptrap that flies with about a third of the public.
(That would be...the RATs)