Okay, here's the set-up first, then the plot:
Twenty-eight years ago, aliens landed on Earth. A corporation known as Multi-National United (also known as MNU) offered to share knowledge about the Earth. Instead, they forced the aliuens to live in communitiies segregated from humans and treated them like scum, while trying to reverse-engineer their technology.
Now, for the plot:
One agent of MNU goes in with a group to investigate the homes of some aliens. He gets sprayed by some alien devide, which proceeds to alter his DNA, changing it to be more like the aliens' DNA. The aliuen technology can only be operated and controlled by someone with alien DNA, so MNU wants to capture the agent and force hium to unlock the machines, so they can reverse-engineer the technology and sell it.