A mutagen virus swept the globe centuries ago as part of a global war. Nobody knows the reason behind the war any longer, but everyone lives in the aftermath of a conflict that hammered civilization into the ground. However, this war created a lingering effect that nobody foresaw: DNA melding. Somehow the mutagen virus created an environment where DNA freely intermingled simply through exposure, creating monstrous and wondrous creatures in the process. Humanity was effected as much as any other, and perhaps more so as the awareness of the change began to set in.
Now, centuries later, civilization is starting to rise from the ashes. Humanity has learned to accept the fact their DNA has intermingled with that of animals, and it is rare to find a human who has "pure" DNA. In fact, to most the fact that they have animal characteristics is normal, and worrying about it is something that most don't have the luxury of time to really worry about while simply trying to survive.
Most people these days exhibit a few animal characteristics of one sort or another, with the most common being some sort of enhanced sense or ability. Originally it was thought that these genetic changes were simply a temporary warping of DNA that would not be passed on through reproduction, but time has proven that theory to be false. These changes appear to be stable and remain true through subsequent generations. There are rumors that people are doing breeding experiments in some parts of the world.
The cities of old are lawless, barren ruins inhabited by bandits trying to live off the scraps of prior generations. Civilization fell into a dark age and is still scrambling up from the ruins. Most technology is bio-organic or mechanical in nature, but limited to muscle powered mechanical devices. There are rumors of gunpowder weapons, but nobody living can claim to have actually seen one function as intended.
Recently, unknown to the population of this world, a deep, secured vault's computers just came online and it began the process of waking deep sleep denizens. This vault was a fail-safe installation populated with volunteers in the event that disaster struck so that humankind might have a chance at rebirth. These denizens may well be the only pure human stock left on the planet, and they have no idea of the world they are about to face.
The game starts with the characters emerging from a newly excavated tunnel that has allowed them exit from the vault. They have made their equipment selections and are prepared for a long-term exploration mission. Their mission is to discover the level of change in the world during the time they were in cryosleep and to report back to the leadership so that they can make a determination on waking the rest of the sleepers.