It looks like they are using elements skipped over in the first part of season 3 from the graphic novel since Tyreese shows up much later in the TV series, while combining it with what has been going on in the graphic novel after the prison. Interestingly enough, there is no sign of the Governor... I expect him to show up at the mid season finale after this mystery killer is found out, and conclude the season with a final resolution. Now that I see how close they are to passing the graphic novel. I understand why they've kept the Governor around. If they proceeded, they'd only have about 2 more seasons of source material.
Anyways... I CANT WAIT!!!!!!!!!!!