This is a personal thing to gauge, but for my tastes, I think a pacing 'gear change' might have enhanced the story. That is, the pace needs to change at the climax. I see the poison reveal as one of those 'stop-time' moments, where every little thing happens in slow motion. That kind of thing takes, as I see it, one of two techniques. First, you can slow down the story before by using more detail when Derek is meeting everyone, then go at normal speed for the killing, or second, go at normal pace and then hyper-detail the effects of the poison. Both ways accentuate the climax and set it apart.
The POV changes in the story without clear demarcation, and that is not a good thing in my book. Everything follows Derek (third person limited) up until the last couple of paragraphs, where things suddenly go omniscient. When I read, I want to become lost in what's called a Reader's Trance, which is where readers become so glued to your storyline that they tune out the rest of the world. Changes in POV can destroy said trance. The most generally accepted way around that is to break the story with a set of asterisks or something like that. Readers have learned to accept this as an indicator that there's been a change in either POV or time.
I offer advice from a rejection email by Eric Flint, author and editor:
(I'm often criticized for using the opinions of successful authors and editors in support of my arguments, but I figure there's a reason they're at the top of the game and we're not yet. So, I'm willing to take it on faith. You can judge for yourself.)EVERY change in viewpoint needs to be preceded by either a chapter break or a line break. There are occasional exceptions to that rule, but not many -- and if you follow it religiously, you won't go wrong. Furthermore, it's almost always very easy to fix. In most cases, it's quite easy to rewrite an episode or a few paragraphs (one, certainly) to keep it in a coherent viewpoint.
So, I felt the need for a change of pace and disliked the sudden POV shift. On the plus side, there's a delightful sense of carefree maliciousness that permeates this story, and that may be enough for many readers.
Nate