A decade after an earthquake destroyed most of Tokyo, what's left of the city is now a large amusement park/prison called Deadman Wonderland which is run by a private corporation. Inmates are forced to wear collars that track their vitals and location.
The prisoners work to earn "cast points" with which to buy food. One high-point game at the park involves deadly obstacle courses that prisoners need to run in front of sadistic spectators.
The story's protagonist, Igarashi Ganta, is your average high school student. By sheer luck he survives the massacre of his whole class at the hands of a mysterious red-robed figure with supernatural powers. As the only survivor, Ganta is accused of being the murderer and is sentenced to death row at Deadman Wonderland.
Like other death row inmates, he wears a collar which releases a slow-acting poison. He needs to do the obstacle course to earn points to buy the candy-shaped antidote.
But rather like the Colosseum of Roman times, these games are fun for everyone except the participants. Will Ganta survive to prove his innocence? And who is the crimson-robed man?
If you can't wait for the anime, the first four volumes of the English version of the manga, published by Tokyopop, are already available. The fifth volume is due out on May 3.