Knightley portrays Megan, a 28-year-old woman in the midst of a quarter-life crisis. The character is without direction and seemingly stuck in adolescence: she lives with her high school boyfriend, and works outside waving a sign for her father's accounting company.
When Megan's boyfriend Anthony (Mark Webber) proposes, she panics and ends up crossing paths with 16-year-old Annika (Chloe Grace Moretz). Megan retreats from the pressures of adult life by hiding out at the teenager's house for a week, and makes a connection with Annika's single father, Craig (Sam Rockwell).
The film is directed by Lynn Shelton, and also stars Ellie Kemper, Kaitlyn Dever and Tiya Sircar. Laggies opens in theaters September 26.