According to Super Hero Hype:
Absolute power corrupts absolutely--and the Guardians time is finally here. Said Johns, The Lantern titles spent the first year of DC COMICS-THE NEW 52 re-establishing themselves, but it all comes back together with year 2 starting with GREEN LANTERN #0 and leading into October's #13's - which share an amazing cover by Ivan Reis. In October, the Guardians' Third Army rises to replace the Green Lantern Corps - but how is horrifying and why will change the Guardians and their ancient mission forever. As we discover what the Third Army actually means, our strongest Lanterns are targeted for absolute destruction. From Atrocitus to Guy Gardner to our newest Green Lantern from Earth - who may have been wrongly chosen - all their darkest secrets and failures will come to light. What is Sinestro's ultimate fate? Who is this new Green Lantern and why was he chosen? What is the Third Army? What with Atrocitus sacrifice to take on the Guardians? What will Larfleeze give up to find the one thing he wants? What happens to Guy Gardner when he's targeted after Hal Jordan? And, most importantly, who is the First Lantern?