Senior citizens Mimi, Bobbi, Virginia and Coralee quietly live out their twilight years in Southern Missouri playing cards and baking cakes. That is until Bobbi’s son-in-law, Jim, cons her into losing her house. Mimi, the unofficial leader of the group, decides to take matters into her own hands, but things spin out of control when she confronts Jim and he accidentally gets killed in the altercation. Having saved Bobbi from homelessness, Mimi and her friends dispose of the body and celebrate. But it isn’t long before local detective, Randy McLemore, is on the case trying to find Jim, who’s been reported missing. Though appearing dimwitted, Randy has a sharp mind and suspects the ladies are somehow involved in Jim’s disappearance. Complicating matters is Harry Lovelace, a criminal associate of Jim who eagerly needs to find him because the man owes him money. Thinking Bobbi might hold the key to Jim’s whereabouts, Harry kidnaps her. When he realizes Jim is gone for good, Harry demands Mimi pay a ransom for Bobbi or he’ll kill her. Undaunted, Mimi rallies her friends to the rescue as Bobbi’s life hangs in the balance by a hardened criminal and the snooping Detective McLemore closes in on them. Things are looking really bad for the ladies, but these are no ordinary women; they are the Grandmothers Murder Club!