The play's name refers to a control city guide sign on eastbound Interstate 10 in California, which indicates that the freeway is headed towards Indio, California, and "other Desert Cities" (that is, the rest of the Coachella Valley and onward towards Phoenix, Arizona).
The play's events occur around Christmas Eve 2004, when the family of Polly and Lyman Wyeth gather in Palm Springs, California. Their daughter Brooke Wyeth returns home after six years in New York writing magazine pieces. Polly's sister Silda is also visiting, out of a time spent in rehab. Polly and Lyman are Republicans, while Silda is a liberal who has fallen into alcoholism. The sisters co-wrote a series of MGM comedies in the 1960s, but have since become estranged chiefly due to Silda's resenting Polly for shifting social worldviews over time.
Brooke announces and presents to her family a memoir recounting a pivotal and tragic event in the family's history: the suicide of her late brother Henry, who had been involved with the radical underground subculture in Venice, and a horrific incident resulting from their advocacy.
During the course of the story, Brooke experiences bitter conflict between her yearning for independent understanding and reliance, and her parents' doting yet secretive motives towards her. During this, she also comes to terms with her family's sorrowing frustration in dealing with her post-divorce depressive episode, even years after Henry's disappearance. Nonetheless, after absorbing the family's perspectives, Brooke insists the memoir is vital for her continuing on in life, whether her family continues to embrace her or not.
In an act of submission from Lyman, he and Polly finally recount the specifics surrounding the recruitment center bombing Henry was implicated in, after years of personal clashes and rejection from both parents and son. Henry showed up disheveled, begging for help and insisting he was unaware of his friends' terrorism. When Lyman insisted Henry turn himself in nonetheless, another argument broke out and Lyman slapped him. Henry disappeared into the night, and wasn't found until three weeks later by Polly. She reveals that she made an interstate trip with Lyman and her son to the northern border, and the ferry he disappeared from. But Lyman painfully reveals they had also doctored Henry's suicide note themselves, and stuck it in his shoes with a tearful goodbye. With their darkest secret unearthed, Lyman and Polly come to terms with their grief, and give Brooke their consent for publishing.
Brooke, in the play's penultimate moment, launches all the pages of her memoir into the air in anguish, screaming of her internal suffering since Henry left her life, and trying to spare her parents the potential pain of her suicide despite her continual grief. Lyman embraces his daughter in remorse.
An epilogue reveals Brooke at her memoir's publishing...years after Polly and Lyman's passing, per their initial request. She recounts a memory of her brother, wondering when she will see him again.
