Now, taken in stride, each sector of the Universe is patrolled by two Lanterns, chosen by the Guardians (and to an extent through the planet-sized Lantern, Mogo) for their ability to withstand, overcome or disavow fear (embodied by the color yellow). Obviously the idea of policement wearing greenish/black/white uniforms and controlling hard light constructs based on a ring exercising an extension of their innate willpower seems a bit silly, but this is a comic. In various adventures, common plot devices ensue, mainly that which separates the Lantern from his ring (which leaves him mostly powerless), depletes the energy of the ring or somehow corrupts the mind/will of the Lantern, making use of the ring difficult or impossible.
The main protagonist of the Lantern series has been for the most part, the human Hal Jordan. A test pilot who saw his father die in a plane crash, Jordan became THE Lantern by which all others were judged, but eventually due to a horrible tragedy, the loss of his family and hence his entire city drove him insane. Possessed by an entity called Parallax (which happened to BE the source of the yellow fear energy) he proceeded to slaughter the entire Lantern Corps and most of the Guardians. This was later revised, Jordan was restored to his former glory and the Corps was resurrected, mainly through the actions of another human, Kyle Rayner, who became Ion, the living vessel of the eponymously named green energy entity that competed with the Parallax creature.
Enter into this Sinestro, arguably the most powerful Lantern prior to Jordan, who due to his own sense of superiority and desire for order was cast out of the Corps (and indeed the matter Universe), became a possessor of the Yellow Power Ring and eventually his own "Sinestro Corps." Recruiting agents capable of generating great fear in response to the Lantern goal to resist it, 2007-2008 was the year of the Sinestro Corps War. Geoff Johns who wrote the saga concluded it with the capture of Sinestro, the 'corrupting' of a Guardian and the discovery of other "Lanterns" embodying different colors relevant to the emotions of the universe (orange for greed, red for hatred, violet for love, etc.).
Now enters in the Black Lantern Saga, wherein the corrupted Guardian "Scar" has created a new faction, powered by a black light energy, which essentially resurrects the dead to feed on the living. Lantern Zombies if you will. Now, for most of us, the cliched yet still appealing concept of the walking dead may seem weird but this has a new spin on it, mainly due to the fact that those killed by Black Lanterns can in turn BECOME recruits themselves. This isn't possible for the other colors, since dead to them is essentially dead. Thus, the Black Lanterns have the capability of recruiting the dead from many other Lantern Corps into their ranks, leading into what is being termed "The Blackest Night" and armageddon for the Universe; life becomes death, light becomes dark, and so on.
The interesting twist to this is that there have been MANY poignant deaths in the DC universe, some quite recently in the Final Crisis saga, and it is the herald of the Black Lanterns--the longtime Green Lantern villain, Black Hand--who seeks out these dead to recruit. So far we've noted a few surprising members: The Martian Manhunter, Elongated Man, and (possibly) Batman, but time will tell. Stretching into next year, this looks to be an amazing ride. The Green Lantern series has become one of my favorites over the past few years, if not one of the more graphic series in play (Black Lanterns recharge their rings not through a battery but from the ripped out hearts of living beings--soul power, if you will) and I am curious to see how it all ties in. Johns was quite successful with his treatments to date, and it remains to be seen how Hal Jordan (who now has been a Red, Orange and Blue Lantern) fits into it all.
I just hope it doesn't have a Dean Koontz ending(1)...
(1): Named for the famous horror author, in which a story spanning several hundred pages is neatly tied up in the last 5-10 pages...the literary equivalent of making love to a beautiful woman and just as you're about to climax, she pulls you out and strokes you to completion into a Kleenex.