Interestingly enough, this Basic Plot of Booker’s does not apply until Part Two of the book, meaning that part one mostly provides background and buildup for the ordeal to come. Nonetheless, the "monster" has been anticipated in part one; for instance, when Alex reads from F. Alexander's loose manuscript entitled A Clockwork Orange. Most of part two has Alex set up to embody the highly feared "monster." In any case, it is definitely something that everyone (except the State, we suppose) fights against, and so is an appropriate "monster."
Picture this. You've become your worst fear – say, a werewolf. You get beat up and left out to die. You stumble towards a random cottage, and a scientist inside is brewing a solution which promises to transform werewolves back into humans. You pinch yourself and wonder, wait, is this a dream? Anyway, that's how Alex finds F. Alexander.
Of course, just when things are going well, complications are bound to arise. In this stage, just as Alex prepares to sign the confession/article F. Alexander has drafted for him as part of their shared subversive plans, F. Alexander realizes that he has unfinished business (personal, of course) with Alex. Thus, instead of executing the original plan (i.e., publish something that makes the Government look irredeemably evil), he comes up with a new plan.
The new plan by F. Alexander and his associates is the nightmare that Alex must confront. Unable to endure the pain of classical music as acquired through his associative learning treatment, Alex has no choice but to leap from a tall building to escape. This is not unlike Winston Smith's confrontation with rats (his #1 fear) in George Orwell's 1984. Can you imagine that: facing your worst nightmare and having to choose between it and…death?
Fortunately, Alex does not die from the jump and instead enjoys a few weeks of being an invalid in bed. His nightmarish journey gains public attention, and the State's doctors work to restore him in an effort to please the public and gain votes for the upcoming election. A clockwork orange no more, Alex is turned back into the evil urchin that delights in violence. The icing on the cake is that F. Alexander has been put away for being a lunatic out for blood.