Nickelodeon has posted the official trailer for the fourth season of the Avatar: The Last Airbender spinoff The Legend of Korra. 
 
Titled Book Four: Balance, the action picks up three years after the last season, and carries the tagline "Can Korra maintain balance in a world that is rapidly changing?"
 
The first episode of the new season will premiere online on Friday, October 3rd (see "'Korra' Returns").