The player awakens to find a world desolate, but not destroyed.
It is at this point that the player recalls the series of event's that lead up to this, starting with that chance conversation.
The player was just taking a stroll, when he happened to overhear a terrorist plot.
Their home town was about to become the target of a nuclear terrorist attack.
Despite their best efforts, the player was unable to stop the detonation.
The resulting events caused a sudden and dramatic change in the world, while there was no real threat to humanity as a whole, the series of events left quite a mark (possibility for inclusion of bitcoins as the currency of the world here)
The player must forge his life anew, and enact his revenge on the people that he destroyed everything he loved.