|Starting Book 4 - Balance|
This takes place 3 years after the end of season 3. Korra is still recovering.. Macco is working as a bodyguard for the soon-to-be Earth King, and Boline is working for a group trying to reunite the Earth kingdom, lead by Kavira. There seems to be a political rivalry going on between supporters of Kavira and the rest of the earth kingdom... people accuse Kavira of colluding with bandits/terrorist to enable her military rule, or something..
Also, suddenly everyone realizes Korra is missing.. she went off on her own and took a new identity. She's still not fully recovered, but is working at a fighting dojo.. she can't go into the avatar state anymore, and sometimes she sees hallucinations of herself in the avatar state attacking her...
although, a dog saw the hallucination too, so it might actually be real? oh.. that dog is actually a spirit, it leads her to this swamp to get her to meet somebody... the person Korra meets is... Taf.. the blind metal bender.