The Memoirs Of A Survivor by Doris Lessing.
Well, this is all very strange. We're in a large city which we are invited to assume is London, after some unspecified catastrophe and the gradual unravelling of civilised society (though some sort of governmental apparatus remains). An unnamed woman lives alone in an apartment in a larger complex of apartments. In quick succession a couple of strange things happen to her; firstly she discovers a strange netherworld which she can gain access to by walking "through" her kitchen wall, secondly she is entrusted with the care of a young girl, Emily, and her strange cat/dog hybrid pet companion, Hugo.
The never-named narrator's experiences behind the wall feature what seem to be scenes from Emily's early life, in addition to some scenes of a seemingly random nature. Things continue to deteriorate in the outside world, Emily acquires a boyfriend who leads a ramshackle gang of youths, things are further complicated by the arrival of a group of feral children who seem to be devoid of any sort of civilised moral instincts altogether (there are grim intimations of cannibalism and other horrors throughout) and Hugo becomes a sort of symbol of the struggle to remain civilised as the children plot to capture and eat him. Eventually the real world and the shadowy parallel world behind the wall come together in a surreal and, frankly, slightly baffling climax.
I've read a few Doris Lessing books before, and this one mirrors some themes developed in the others: a slightly paranoid sense of powerlessness, of circumstances being controlled by a shadowy group of "others" (dealt with much more explicitly in Shikasta and the rest of the Canopus in Argos series, and, in a more straightforward way, in The Good Terrorist), the richness of the inner world of the imagination, and the blurring of the boundaries between it and the "real" world (this is the theme of the powerfully weird Briefing For A Descent Into Hell - probably the best of the small subset of her work that I've read). Apparently a lot of her 1970's output was informed by Doris Lessing's involvement with Sufi Islam, this period includes all of the books mentioned above (with the exception of The Good Terrorist, which was written in 1985). (Strangely enough Richard Thompson who featured briefly in a recent post was also an adherent of Sufism.)
Doris Lessing apparently described The Memoirs Of A Survivor as "an attempt at autobiography". If that's the case then are we to assume that in addition to the "folding" of time that enables the narrator to see scenes from Emily's childhood, that perhaps some further "folding" of time is going on to enable the narrator to witness herself as a young woman - i.e. that the narrator and Emily are the same person? And what are we to make of the ending, with its exotic fantasy world of flourishing wildlife, giant iron eggs, and space and time seemingly collapsing in on itself? Search me, guv. But for a book of less than 200 pages it's a powerfully rich and strange experience, and I'm of the opinion that being baffled from time to time is good for the mind.