VERONICA’S ROOM by Ira Levin
Susan Kerner, a young Boston college student and Larry Eastwood, a young lawyer she's just met, have been enticed to the Brabissant mansion by the Mackeys, a charming, elderly Irish couple who are struck by Susan's strong resemblance to Veronica Brabissant, long dead daughter of the family for whom they work
They view Veronica's picture in her room, untouched by time. Susan's induced to impersonate Veronica for awhile to solace the only living Brabissant, her addled sister living in the past and believing Veronica's alive and angry with her
But once dressed in Veronica's clothes, Susan finds herself locked in the role and locked in Veronica's room. Or is she Veronica, in 1935, pretending to be an imaginary Susan?