Unthinkable (Bitter Reward) (2007)

Overdomineering female police detective Jamie McDowell still tries to run her 19-year old only son Peter's life although he is a builder who lives alone. She strongly opposes his engagement to Kelly Shaw, who he doesn't know very long, and forces him to bring her to diner, where Jamie and mother Susan Shaw repeat that mistake. After Kelly provoked her ex-fiancé Ray Rankin in a bar 'to test Peter's love' again, they part in anger. That evening the mothers, who went out together, find Kelly burnt to death in Susan's house; an expert clearly concludes arson. To her horror, Jamie quickly finds the evidence seems to point at one logical suspect: her son Peter...