One of the unexplained mysteries from the Doctor Who season finale is revealed in this short scene. The Whispermen launch their campaign against the Doctor with a strange visit.
This is being listed as a "prequel" to "The Name of the Doctor." I'm not sure if it was meant to be shown as a prologue, like "She Said, He Said" and was ultimately dumped, or if it was a scene meant for the episode itself that didn't make it in. Either way, it explains the message delivered by the prisoner Clarence in the episode.