The news is a rich source of story material. Take a look through the news items in your paper, any online news source, television, or radio. Pick one of the news events and write a story based on the event having a much different cause than what was reported. In other words, give them a story that is a bit more fantastic than the truth.
Another interesting aspect of this prompt is that the genre of the story you are planning to write will affect how you interpret the news items. The unfortunate news of a commuter train derailing will generate a much different story for romance than it will for a mystery or an action/suspense novel.
The news item I used for my example involved the trading of political prisoners.
Based on that idea I generated the following elevator pitch.
Catch and Release – The President orders the military in Afghanistan to start secretly releasing dangerous prisoners in exchange for information from the terrorists about their rivals. On the surface this looks like a standard political move, but it is really a vicious program of annihilation. Each of the released prisoners has been infected with a virus that will spread death to the terrorist network and their families. The situation changes when several of the service men return home and die from the same engineered virus that they are supposed to be immune, except that this mutated strain no longer targets people that share DNA with the carrier.