I've got this idea for a steampunk setting, but, not being that familiar with steampunk genre conventions (I just enjoy the aesthetic), I could use (and appreciate) some ideas for fleshing it out a little more.
High pressure steam engines were actually invented by mice in the mid 18th century, but the designs were stolen by humans. Mice have developed a vast empire based on the steam engine. Mouse society mirrors much of humanity’s, however they have advanced technology even further than humans know. Mice have tamed the ether, developed their psychic potential, and have had analytical engines for decades. Most of the human population does not know of the mice’s contribution to their society, but those that do, look to mice for more advanced technology.
The Society for Human Technological Progress, is a secret society that studies mice and tries to learn from them. Unfortunately, its methods are rather extreme; capture and torture (explained as experiments on lab mice to the general human population). Of course, various members of the Society will claim the inventions as their own to keep up the masquerade.
Mice do have a few things to their advantage. Humans haven’t discovered their greatest technological achievement, the Death Ray. The Death Ray appears as a bright light and has a very high destructive potential. The Death Ray is most often used by Knights of the Claw, an international organization made up of mice who devote themselves to protecting mouse society from humans.\
Some mice, instead of studying the laws of the physical universe, have studied the mysteries of the mind. They have learned how to control their minds to such an extent that they can manipulate physical objects using only their minds. It is said that some can even control the minds of others, but that is generally considered a story told to frighten pups.
In addition to the threats from humans, it is also a time of social unrest in mouse society. For centuries, mice have had a strict class based society. Now the members of the working class are organizing and demanding equality with the ruling class. The ruling class is pushing back with the Secret Police.
Recently, since the invention of the automole, affluent mice have begun building underground cities to live in. However, since the time and effort of making an underground habitat is great, many of the poorer mice cannot afford to live underground and survive on the surface as best they can. Living on the surface is dangerous not only because of the Society, but also the general human populace looks upon mice as pests. Even the wealthy mice have to venture on to the surface when they need to travel to other locations. Although efforts are being made to connect major underground cities by underground rail roads, providing safe travel to those that can afford it.
The lower class mice are growing very jealous of the upper class because of their relative safety in underground cities. The entrances to the cities are usually heavily guarded against intruders. The various outbreaks of bubonic plague from the mid 4th century all the way through today are actually wars waged between mice and men, especially the Society. Human propaganda tells the populace that it is fleas transmitting the virus from rodents to humans, but it is actually the development of anti-human weapons by the mice.