From the website:
This short FREE Quickstart adventure is designed to allow players to take on the role of heroes from the John Carter of Mars stories as they encounter perilous adventures on Barsoom explore the rules of its 2d20 roleplaying system.
The adventure is set shortly after the events of A Princess of Mars and the decline of Helium’s long time rival, Zodanga. During this period, John Carter stays for years in Helium with his beloved Dejah Thoris, but few of his adventures during this time are described in Burrough’s work.
As the adventure begins, Carter is travelling with Dejah and several friends and allies by flier to meet with a delegation from a minor Red Martian kingdom, Voninka, that is seeking alliance with Helium. Voninka was a small satellite nation of Zodanga until the nation’s recent defeat at the hands of Helium. It now seeks new allies among Helium and its jeddak, a young but respected leader known as Corlan Nim, has requested a diplomatic meeting with representatives of Helium—the player heroes and their crew.
But all is not quite as it seems and this apparently simple diplomatic mission soon launches our heroes into a whirlwind adventure!
Prepare to experience the might and majesty of 2d20 adventures on the red planet in John Carter of Mars!