The subject is not really new.In her last film "Two-Faced woman" ,Greta Garbo played "twins" (but actually there was only one woman) with different personalities.More interesting was Siodak's "the dark mirror" where Davis' good friend Olivia de Havilland played twin sisters too,one of whom was suspected of murder.
Twins were certainly trendy at the time since ,the very same year as De Havilland,Davis tried her hand at the subject,not in a thriller,but in a melodrama.Davis was as subtle an actress to portray two different women.One of them is an artist ,a romantic loyal woman ;the other one is a real bitch,who steals her sister's boyfriend (Glenn Ford).
There are scenes with an "accursed " anarchist artist who becomes Kate's teacher cause he thinks her painting is lousy.The reason,he says ,is that she was never a real woman (like sister Patricia ,maybe?)Those scenes with Karnock are mostly filler,and the film becomes interesting again when Kate pretends to be Patricia,although these scenes show more than a distant resemblance with "Two-faced woman" by Cukor.
Not a major Davis movie,but interesting for her numerous fans.