When Tommy, a garage mechanic, defends his girlfriend in a bar fight in a Native American reservation in Oklahoma, the entire bar, along with everyone inside, is sucked into a shuttlecraft. They are transported into The Sphere, an enormous, organic alien ship. Tommy is set free by one of the denizens and his task is to save his girlfriend Jen and grandfather Enisi, and find out what the meaning of The Sphere is.
This 3D-shooter, based on a modified version of the Doom 3 engine, takes place entirely inside the gigantic ship. As a combination of organic and cybernetic structures, gravity is defied: with the proper grids activated, you can walk on walls and ceilings. There are also multiple dimensions inside the ship you can cross using portals. During his quest, Tommy struggles with his Native American lineage. The ghost-like hawk Talon is always on your side and you sometimes cross over to another land to get help from your grandfather. Tommy can also shift to Spirit Walk, an alternate dimension in the game to get past obstacles and solve puzzles. When you die, you are also transported to another realm where you have to shoot lost souls with your spirit bow before being sent back. Your new health and spirit status will be based on your performance there.
The weapons Tommy uses are usually organic, with secondary fire functions. The arsenal includes a wrench, a rifle, crawlers, an acid sprayer, an auto cannon, a leech gun (chargeable with fire, ice, red orbs or lightning), a rocket launcher and the spirit bow. Certain parts of the game require you to explore large areas in a flying pod. You can use it to engage enemies or use the tractor beam to move objects. Navigation, often with a distinct lack of direction, is reminiscent of Descent then. Puzzles usually require you to decipher codes, activate switches and find entrances.
The game supports OpenAL and EAX HD surround sound, and multiplayer games for up to eight players in duel or team deathmatch. Although the game is developed by Human Head Studios, it is produced and was originally designed by 3D Realms.