Anna Kendrick and Blake Lively are spot on as two very different moms who become best friends.  This is a rare comedy thriller that works on both levels.  Paul Feig adeptly directs a snappy script by Jessica Sharzer, which was adapted from a Darcey Bell novel. We open with Anna Kendrick playing perky helicopter mom, Stephanie, who dishes helpful household hints via her vblog.  She is extremely  energetic and her vblog has a growing following (though her local “friends” from her son’s school find it, and her, as something to make fun of, due to her very  overinvolved personality).  Lively plays the drop-dead beautiful Emily, the fashion diva who asks the comparatively “plain” Stephanie to share a martini while their sons have a play date.  They have absolutely nothing in common, but Emily intrigues Stephanie with her brash and very earthy attitude.  Soon, Stephanie finds herself more and more involved with Emily, while wondering why they have become best buds in just a few short weeks.  Emily increasingly asks Stephanie to watch her son and she becomes more and more involved, meeting Emily’s sexy husband (Henry Golding) and becoming virtually a nanny.  Then, Emily calls with an emergency, and can Stephanie come yet again to watch both kids, which is the simple favor of the title.  As you probably can guess, Emily disappears leaving her son and sexy husband behind.  Sephanie begins to suspect that Emily she wasn’t who she appeared to be when a body is found!  What?!  The rest of the movie is compelling film-noir, with lots of twists, double-dealing and enough secrets to keep you guessing until the deliciously satisfying ending.  Yes, it is a little over the top, but so what?  This movie is so entertaining that you won’t even notice.  If you liked ‘Gone Girl,’  you are going to love ‘A Simple Favor!’