Why Did Rowena Kill Grace?

While the film's events have Rowena investigating Hill out of suspicion that he killed her to keep her from exposing his infidelity, the film's conclusion revealed that Rowena was her true killer, with the revelation also leading to Grace's posthumous reveal as a blackmailer.

Did Rowena kill Grace?

But in the film's climax, after Hill was arrested and convicted for Grace's murder, it was revealed that it was Rowena who had killed Grace and used the investigation into Hill to cover for herself, with her villainous reveal occurring when she revealed she was hiding a bottle of belladonna in her medicine cabinet.

Who is the bad guy in perfect stranger?

Rowena "Ro" Price is the main protagonist (and later revealed to be the main villain) of the neo-noir crime thriller, Perfect Stranger. She is portrayed by Halle Berry.