The third season of the American science fiction television series Fringe began airing on the Fox network on September 23, 2010, and concluded on May 6, 2011. Twenty-two episodes long, the season was produced by Bad Robot Productions in association with Warner Bros. Television, and its showrunners were Jeff Pinkner and J.H. Wyman. Lead actors Anna Torv, John Noble, and Joshua Jackson reprised their roles as FBI agent Olivia Dunham and the father-son duo Walter and Peter Bishop. Previous series regulars Lance Reddick, Jasika Nicole, and Blair Brown also returned, along with recurring guest stars Kirk Acevedo, Seth Gabel, and Ryan McDonald.
Building off the finale from the previous season, Fringes third season dealt with a war between the prime and parallel universes. During the first part of the season, odd-numbered episodes mostly took place in the parallel universe and have a red title sequence, while even-numbered episodes mostly took place in the prime universe and have the original blue title sequence. In episode eight, "Entrada", the title sequence is a mixture of blue and red to signify the universal focus of the episode. In the rest of the season, however, the episodes focus on the prime universe with brief shifts to the parallel universe.
Wyman and Pinkner saw Fringe as two shows, where they could provide a detailed mythology that was equally compelling in both universes. Eager to explore "what-if" moments, historical idiosyncrasies and other differences were inserted to help disambiguate the two worlds. Much of the season was designed around a doomsday device, as they believed its mysteriousness was "a great story engine for us." The nineteenth episode, "Lysergic Acid Diethylamide", contained long sequences of animation in order to accommodate guest actor Leonard Nimoy's retirement from acting. While the writers had attempted to continue the idea of the "mythalone" for both casual and devoted fans, Fringe mythology became more visible in the last episodes of the season. Equating the final three episodes to a chapter in a novel, the writers "linked [them] in one continuous story arc."
The third season was positively received by television critics, and it earned 77 out of 100 on the aggregate review website Metacritic, indicating critical reception as "generally favorable." Reviewers reacted well to the exploration of the parallel universe, and the performances of Torv and Noble, who each played differing versions of their original characters, were lauded. Fringe ended its third season with an average of 5.83 million viewers per episode, placing 99th for the network television season. The New York Times called the series "the best major-network show that no one is watching." Despite its low ratings, Fox renewed the series for a fourth season on March 24, 2011.
Season summary
Following Peter's rescue from the parallel universe, the prime universe Fringe team comes to learn of the Wave Sink Device, the machine that Walternate was attempting to use to destroy the prime universe. They are unaware that Fauxlivia has replaced Olivia, and she works to help the Fringe Division to identify the components hidden across the globe for a similar Wave Form Device in the prime universe. She also gets romantically close to Peter.
Olivia is held in Walternate's laboratories in the parallel universe, and given drugs and conditioning to make her believe she is Fauxlivia, and subsequently a willing test subject for Walternate's tests of the powers of Cortexiphan. Olivia slowly breaks this conditioning, and on one trial, is able to cross over to the prime universe to relay a warning to Peter about Fauxlivia. Her identity exposed, Fauxlivia is extracted back to the parallel universe by Walternate's shapeshifters, while Olivia gets help from the other Broyles to cross back to the prime universe. Olivia is distraught after her return, knowing about Peter's relationship with Fauxlivia. However, after some time, the two reconcile and admit they have feelings for each other.