I saw this website a while back that had made a FATE Core hack for Secret of NIMH. In his game, you play special mice/rats that have been altered by NIMH. The website is at https://taoofchall.wordpress.com/2013/06/01/fate-core-secret-of-nimh/ if you want to check it out. It is an old post, a couple of years old in fact, but as soon as I found it I found myself wanting to run a campaign in that setting. But since my groups are not eager to abandon the games they are already playing, I settled for writing this intro adventure.
This adventure, intended to be a one shot or an introduction into the campaign, is designed for 4 players running a mix of mice and rat characters. In this adventure, the characters will have to escape their cages, survive their trek through the woods, negotiate with the Great Owl, and find their way to Thorn Valley.
Note that Fight, Shoot, and Provoke are never emphasized as options. This is on purpose, as this adventure does not feature any combat. Mice and rats are small and surrounded by predators. Attacking is always a bad idea in this adventure. Later, when they have crafted weapons and have a better understanding of what they are facing, combat will probably be ok. But that’s assuming that you wish for this adventure to continue into a campaign. As a one shot, definitely discourage players from building characters with these skills at the top of their track.