In the style of one of the books. Canon, set somewhere in the 30s. Marco's POV. Modern-day, because I always wondered what would happen if the series took place now, but higher content rating, because I always found it silly how the kids would supposedly say "kick Yeerk butt" or whatever.
The gist: While trying to cheat on a PSAT practice test, Marco spots a kid in his class in Joe Bob Fenestre's anti-Yeerk chat room. The Animorphs decide to listen in and eventually talk to Fenestre directly. He tells them about a plot by the Yeerks to expand from California, building an auxiliary pool in an abandoned subway tunnel. He asks for the Animorphs' help.
FFN link:
http://www.fanfiction.net/s/9800206/1/The-Rogue (I can post in other formats too, just let me know)
This is actually the first piece of fanfiction I've ever written, although I've written a lot of other stuff (oh lord, have I written a lot of other stuff), so this is kind of cool for me.