Complete story — includes the ending
The Fringe team desperately attempt to prevent William Bell from destroying their universe to remake it in his own image. Bell utilizes Olivia's cortexiphan abilities to finish the process and Walter Bishop is forced to shoot and kill her to stop the destruction. As hinted in the previous episode, cortexiphan has regenerative abilities and the high content in Olivia's body allows her to heal from the deadly shot, which happens after the danger to the world has passed.
Sources and content license
Source and revision history · Adapted from Wikipedia contributors, Fringe season 4. HTML formatting and reference markers removed. · Content license