We squoze this Netflix DVD in New Year's Eve, waiting for the ball to drop. By the way, I am not sure why we do that ball-drop thing any more.
IMDB genrecizes this as Comedy/Crime/Drama, which is about right. The five-foot-two Pride of Portland ME, Anna Kendrick, plays Stephanie: a seemingly perfect single suburban-CT mom with a mildly popular "vlog" where she perkily shares recipes, crafts, and homemaking tips. Her cute son, Miles, demands a play date with his new friend Nicky, which kicks off her involvement with Nicky's mom… well, let's call her "Emily", since that's her name in the credits, played by the 5-foot-10 Blake Lively. Emily is foulmouthed, hard-drinking, rich, and, uh, oversharing. Significantly, even with her salary as a NYC PR person for a glitzy fashion company, and her hubby's teaching gig at a local university, she claims to be on the edge of financial ruin.
One day, Emily asks Stephanie for the titular "simple favor": could she pick up Nicky from school and watch him for a bit? Fine, but Emily doesn't appear later to pick Nicky up. Or ever. She goes missing. What happened to her?
From there, the story takes a number of unexpected twists. No spoilers here, at least none other than you can get from the blurbs. A lot of R-rated fun (involving, according to the MPAA, "sexual content and language throughout, some graphic nude images, drug use and violence").