Mists of Pandaria is just a week away from release and Blizzard are leading WoW players into it with the launch of the game's first scenario, Theramore's Fall. The scenario will leave the world (of Warcraft) forever changed. If you want to get involved you better read on.
The wily chaps and chappettes over at MMO-Champion spotted the scenario's activation, saying that it will run from the 17th (today!) till the 24th.
Theramore's Fall is the first scenario to appear in Blizzard's life-encompassing MMO, though they're pegged to become a regular feature. Each scenario will run for a limited time and will bring with it a new questline, with new enemies, bosses, and equipment drops, and a permanent change to the WoW world. Theramore's Fall will still be playable after this week, but it will become locked out to anyone below level 90 (the new maximum level). Even then, a future patch will phase out the scenario entirely.
You won't be able to play the game solo, instead "For the duration of the week of September 18-24, level-85 characters will be able to queue up for and participate in the Alliance and Horde versions of this new Scenario with two friends. (Please note: if friends are not available to you at the time, two will be provided. Batteries not included. Subject to change. Void where prohibited.)"
Simply boot up the game and make your way over to the Isle of Theramore.