My favorite concept for distopian future would be Dolphin Takeover. Consider the intelligence of dolphins. As far as we are aware, the can form complex thoughts but lack appendages that can wield tools. As such, there is no written language or dolphin made structures. Well somewhere down the line, those dolphins will learn to use tools. Then, deep underwater where we can't monitor them, they will build. An enormous civilization. They will learn to fight, to kill.
As soon as nuclear fallout or some kind of crisis occurs, they will strike. We human will have no idea what to do against this sudden threat. Our only hope would be the whalers, which we try so hard to remove. Perhaps dolphins have manipulated our government already to protect their interests. Either way, dolphins are coming. Study up on dolphin weakpoints and water tactics.
You'll need it.