Westopolis is a human city left in ruins from the attacks of the Black Arms, filled with roads and skyscrapers. Much of the area has collapsed from the explosions of the Black Arms' attack.
After Black Doom appearing before him as the Black Arms invade Westopolis, Shadow the Hedgehog rushes into the city in his search for the Chaos Emeralds. He quickly runs into Sonic the Hedgehog, who asks him to help fight the Black Arms throughout the City, before grabbing the first Chaos Emerald in the midst of the stage. Doom's Eye appears to him not long after, demanding that Shadow instead kill the G.U.N. soldiers defending the city. The neutral path involves going straight to the Chaos Emerald located at the end of the stage.
There is a hidden area to the right, just before the Jump Panel that leads to the second checkpoint. The player must jump over the pit to reach the platform on the other end with the key.
A pulley can be found shortly after the second checkpoint, which must be used to reach the second key.
Just before the third checkpoint, two Gun Beetles can be seen hovering by a platform. The player must quickly Homing Attack the enemies before they are destroyed to reach the platform with the third key.
There is a gate directly to the left of the third checkpoint. The player must Slide or Spin Dash under it and break the container in the back to get the 4th key.
After the Goal Ring are a set of Jump Panels that lead to another skydiving section; the final key can be seen on the right side.
A Sub-Machine Gun and a G.U.N. HMMWV can be found behind the door, which is located immediately to the right of the fourth checkpoint.
To complete the Normal Mission, all that is required of the player is that to reach the Goal Ring with the Chaos Emerald in it. Missions like these did not require the player to finish of any of the Black Arms or GUN Soldiers, but sometimes defeating them will make it easier for the player to get through the Stage faster.
23 Black Arms should have been defeated by the time you reach checkpoint #2, 29 by checkpoint #3, 33 by checkpoint #4, 42 before checkpoint #5, and all 45 before the final checkpoint.
The stage is a little more difficult to get A ranking, because there are more enemies to defeat. If the player use Chaos Control the player may miss few. Another aspect of the Hero Mission that is absent from the Dark Mission is that some enemies fall from the sky. If the player go to quickly through the stage, the player may miss some of them.
If one were to play with Sonic with a second controller, not only does he Homing Attack Black Arms, but he can also hurt GUN Soldiers with it. He seems to function more like Shadow than other hero characters; he can activate switches, put out fires, open locked key doors, and he even has a scripted Sky Diving sequence which can be done at the end of the level.
Strangely, if the player is running at full speed with Sonic and then pulls the control stick down to skid to a halt he shares the same hovershoe sound effects as Shadow when he brakes.
The hint bubble where Sonic suggests to Shadow that they use the homing attack on GUN beetles to cross a gap was originally supposed to have Sonic use the word "piss" (i.e., "Hate to piss off GUN..."), but it was changed to "tick" in the final version.
If a laser fires during the Doom's Eye intro scene, the crates underneath said laser will remain intact.