"Brown Betty" is the 19th episode of the second season of the American science fiction drama television series Fringe, the 40th overall episode of the series, and is the only one of the series performed as a musical. The episode was written by co-showrunners Jeff Pinkner and J. H. Wyman, and consulting producer Akiva Goldsman. It was directed by filmmaker Seith Mann. As the episode begins with Peter's continued disappearance, Walter consoles himself by smoking a strain of marijuana called "Brown Betty." Most of the episode is then told from his drug-addled perspective, in which Olivia is a 1940s noir detective and Peter is a conman who ran away with Walter's glass heart.

The second season of the American science fiction television series Fringe commenced airing on the Fox network on September 17, 2009, and concluded on May 20, 2010. The season was produced by Bad Robot in association with Warner Bros. Television, and its showrunners were Jeff Pinkner and J. H. Wyman. Actors Anna Torv, John Noble, and Joshua Jackson reprised their roles as FBI agent Olivia Dunham and father-son duo Walter and Peter Bishop, respectively. Previous series regulars Lance Reddick, Jasika Nicole, Blair Brown, and Kirk Acevedo also returned, though with Acevedo in a limited capacity.