First, congratulations! Your agents sound like a ton of fun, and your writing sample is entertaining, except for a few mechanical issues. VM says July is going to have some detailed concrit for you, so I don't want to jump the gun by getting into all of it, but I do want to talk about semicolons.
Your writing sample is roughly six pages long. As a rule of thumb, that means you get to use about six semicolons, no more, preferably fewer. You used 23. It's excessive and it's distracting, especially since many of them are not used correctly. A lot of them would do perfectly well as commas, some of them properly ought to be colons, and the rest could probably be taken out in favor of a period and a new sentence. To give some examples:
1) "It’d been about three days since Agent Skeet had been on a mission; an unusual circumstance in the PPC."
- This one should be a comma. It makes just as much sense, and the end bit of the sentence is a fragment that can't stand on its own. A semicolon implies that you're connecting two thoughts that could stand alone but are closely related, but this isn't a separate thought, it's a continuation of the one at the beginning.
2) "The message flickered up on the screen;"
- You're introducing a quote here, so this 100% absolutely needs to be a colon. Never use a semicolon to introduce anything. That is the colon's one and only job.
3) "She clambered to her feet and began re-gathering everything from the floor around the doorway; Skeet recognised many of the typical newbie gifts; shiny things, sweets and assorted Bleep-products."
- The first semicolon there is sitting at what should be the end of a sentence, and I'd say even the end of a paragraph. The first bit is Amelia's action and should be part of her paragraph. The next bit is Skeet's action and should be part of his paragraph. Generally speaking, if you change doers, you should change paragraphs.
- The second semicolon there should be a colon, because you're introducing a list. The colon is a hard-working but highly specialized little guy who just wants to make a decent living introducing stuff so he can feed his family. Don't let that flashy up-jumped jackanapes, the semicolon, take that away from him.
The semicolon is a delicate and tricky little devil, tempting in its versatility, but like most temptations, it should be resisted except on special occasions. I went through a phase of overusing them myself, and have since read a lot about them and learned to feel where they work and where they really aren't necessary (read: most of the time). I'm happy to talk about it more if you have any questions. {= )
See also:
http://ppc.wikia.com/wiki/Punctuation#On_Semicolons~Neshomeh