SPOILER ALERT: this blog post gives a general indication of how the film ends.
I loved this movie, and I'm afraid it will be misunderstood.
It's a suspense flick with a story Alfred Hitchcock might have admired. A normal guy--actually gal, played by Anna Kendrick--crosses paths with the wrong person and gets in over her head. She has to investigate and ultimately do some double-crossing of her own to undo the villain and return to her good life.
We could be talking about Strangers on a Train or North by Northwest, only funnier.
It might be misunderstood because some critics are describing it as neo-noir, and it is not noir. It may have some things in common with classic noir novels and films, including a life-insurance scam. But the main character is not a loser ultimately done in by her own greed and stupidity.
So go and see it, and enjoy the chemistry between Anna Kendrick, Blake Lively, and Henry Golding.
And don't confuse it with another movie that has a similar title, A Simple Plan. That one really is noir.