A few of the Mutants have found a way into the city dome. If many more of them break in, we shall be overpowered and will have to evacuate the dome. And then what? Become Mutants ourselves?
But you can't let that happen! You must find their secret entrance and seal it off! No one else has been able to do this. But you can. We know you can.
Notes
The MS-DOS version seems to date from 1987. It is copyrighted 1982 & 1987, suggesting that the game might've appeared on a different platform earlier.