A Simple Favor (2018)

A single stay-at-home mom, Stephanie (Anna Kendrick), runs a popular vlog out of her New York City home that discusses all kinds of homemaker and cooking ideas (a la Martha Stewart). One day while picking her son, Miles (Joshua Satine), up from school, her son wants to invite a school friend over - Nicky ((Ian Ho). While dismissing her son's demands, Stephanie meets Nicky's mom - a mysterious glamorous, beautiful woman named "Emily" (Blake Lively).

After talking to Emily, Stephanie agrees to let Nicky come over to play. Stephanie becomes quick friends with Emily and starts visiting Emily's glamorous home where she learns Emily is a foul-mouthed, bi-sexual alcoholic who may or may not be married to Sean (Henry Golding), who is a washed up novelist. They have been having financial difficulties for several years. During one visit, we learn Stephanie had a husband and step-brother who both died in a suspicious car accident several years ago. Stephanie also reveals a possible incestuous fling with her step-brother when they were much younger.

Eventually, Emily is asking Stephanie to regularly take care of Nicky so she can take of some "business." During one such request, Emily does not return. Stephanie calls everyone she knows and no-one knows where Emily is though she is known to have left town in a rental car. After 5 days, the police discover her rental car in a summer camp lake in Michigan and some divers discover her dead body in the lake; her body is positively identified by tattoos and DNA.

After the funeral the police start investigating the mysterious death and Stephanie starts her own investigation. Nicky begins seeing his mom at school but his visions are dismissed. Sean and Stephanie begin a sexual relationship and she moves into Sean's home, which makes Stephanie a suspect in Emily's death (in the eyes of the police). Stephanie visits the summer camp and learns "Emily" is an identical twin with the real name of Faith. Her twin sister's name is Hope. Stephanie also learns there is a $4 million insurance policy on Emily's life that Sean will collect, which immediately makes Sean a suspect.

Stephanie visits the painter who painted a pornographic painting of "Emily" and learns she called herself Claudia (her real middle name) when sitting for the painting. She also may have had a fling with the painter. Stephanie finds and visits "Emily's" mom and dad and learns that the twins burned down their family home when 16 years old and have been on the run ever since. Stephanie calls the insurance company to tell them Emily has a twin and Emily may still be alive. When "Emily" appears to Sean at a restaurant, we learn she never died and faked her death to collect the $4 million insurance.

She reveals to Sean that she has a twin sister whom she killed at the lake to fake her death but that is now all for naught since the insurance company is not going to pay the $4 million until they conduct a new investigation. She hatches a plan, with a very reluctant Sean, to get rid of Stephanie. Emily (Faith) and Stephanie meet for martinis in a graveyard and Emily reveals her life story and her whole plan to fake her death and collect the insurance because of the financial difficulties though she says her twin sister drowned on her own.

In the final scenes, Sean, Emily (Faith) and Stephanie meet at Emily's home. Emily and Sean want to meet Stephanie to carry of the plan to kill her and Stephanie agrees to meet with the ulterior motive of trying to get Emily to admit to killing her sister and faking her death (she brings a gun along, just in case). During the meeting Stephanie changes the plan and shoots Sean, but the gun is purposely loaded with blanks to fake Sean's death (since Stephanie loves Sean). Emily sees through the ruse and pulls out her own gun and really shoots Sean, but just wounds him.

Stephanie tricks Emily to admitting to killing her sister and reveals she is wearing a button camera and recorded everything on her vlog. They hear police sirens in the background and "Emily" runs out of the house and is immediately struck by a car driven by one of Stephanie's friends - though hurt she is not killed. She is arrested, tried and convicted of killing her sister and insurance fraud. Sean is convicted of insurance fraud. At the end of the movie we see Stephanie on her vlog that now has 1 million subscribers due to the publicity of the investigation.