In this episode, citizens are beginning to spontaneously self-incinerate as pawns in a larger game to alter mankind's destiny. The Boston Metropolitan Area faces immolation as the power of the sun is focused on the fossil fuels below Eastern Massachusetts.
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The various fringe events in this two-part season finale were engineered to bring out the strongest aspects of Olivia's powers for William Bell to use.
The Observer can be seen behind the ambulance prior to Walter and Astrid being given access to the crime scene.
A sign for "Liberty Wind Chimes" in 'Worlds Apart' contains the Liberty Bell in its logo, hinting at the return of William Bell in 'Brave New World' (Part 1)'.
Signage saying "Eden" on the exterior of Bell's waterfront warehouse in 'Brave New World (Part 1)' foreshadows his mission to create a new, pristine universe with new creatures in 'Brave New World (Part 2)'.
In "Brave New World (Part 1)" Walter learned that William Bell was really behind everything. (Image 1)
Walter sacrificed Olivia, the most valuable piece in the game, in order to save the world in "Brave New World (Part 2)".