Jane Gaskell’s 1957 Strange Evil is a stand-alone free love portal fantasy.
Professional model Judith Henderson is enormously put out to discover that her cousin Dorinda has invited herself to stay with Judith. This is the first Judith has heard of Dorinda, Dorinda’s mother having vanished following a scandalous marriage to an Italian aristocrat. Judith has little choice but to host Dorinda while Dorinda visits her mother’s birthland.
Judith soon discovers that there’s an upside to the unwanted guest. The guest has brought her fiancé, Zameis, with her. Judith is immediately besotted with Zameis.