Denise Miller usually goes by the name Dennie. It is 1970, and the twenty-year-old is hitchhiking home after leaving a hippie colony where she has been living for a while. She is tired and dirty; the first thing she does when she reaches her childhood home is wash her feet off in the pool, before going inside and falling asleep in the bed she slept in as a child. As she has not told anyone she is coming home, her parents and younger sister Susie are oblivious to her return and carry on their life as usual; their parents wake Susie for school, she gets ready with her usual attitude, before finding Dennie in her old room and alerting her parents that she is home.
It is a joyful reunion; stressed out parents are happy to see their prodigal daughter and Dennie promises to say home in the future if her parents will just forgive her for leaving. They try, but they are constantly terrified of upsetting her lest she disappear again. By contrast, Susie cannot put a foot right, and Dennie realizes that her little sister and their parents have been experiencing a great deal of discord in their relationship. Susie is growing more rebellious and there are constant arguments.
Meanwhile, the boyfriend that Dennie has left behind in Los Angeles, at the hippie colony, is none too pleased that she has left him. He is determined to find her and bring her back to live with him again. He steals a truck and stops at a diner where he eats and leaves without paying the bill. He then leaves the first stolen truck in the parking lot and takes an ice cream truck instead. Police follow him as he goes to find Dennie.
Dennie is cleaning herself up, both literally and metaphorically. She starts to look like the Miller's middle class little girl again, helping out in the house and following the rules. She seems traumatized by her hippie life, which we see in snatched flashbacks of her being hungry, begging on the street and doing drugs. This is the lifestyle her parents are terrified that Susie is falling into as well; they turn her bedroom upside down looking for evidence of drug use and there is a monumental screaming match when Susie returns home to find her room looking like a tornado has come through it. Dennie begins to share her parents' concern about Susie and starts to look for drug paraphernalia throughout the house, not just in her sister's room. When she finds Susie's secret stash of pills she confronts her sister and tells her that she can't handle drugs, even if she thinks that she can.
Dennie helps her parents host a party for their friends in the neighborhood. Everyone is please to see her home, and seemingly back to the "normal" kid they knew. She watches as the adults get more and more drunk, and start to lose their polite inhibitions with each other. The party gets loud and lascivious. Upstairs, Susie gets high. When she comes downstairs she shakes the gathering up with her drug fueled antics that mortify her parents and drive Dennie to a level of stress that she cannot handle. She dives into the pool in her clothes and swims laps, to the amusement of the guests
Dennie's boyfriend arrives at the house the following day. He climbs up a tree by the pool and announces to Dennie that her family is messed up and dysfunctional and that in order to escape it she should follow him to Canada. They begin to make out, but when her parents realize that he is at the house, they begin to yell at Dennie. She runs to her room and hides out, emotionally unable to cope with everything happening around her. Her boyfriend jumps into the stolen ice cream truck and leaves. When the Millers go back into the house they realize that Susie has followed in her sister's footsteps and run away with her own boyfriend to join a group of hippies. Dennie, meanwhile, has turned off her emotions. We see her at the end of the movie, her face set without expression, vacuuming, just like her mother.
