Berta Isla and Tomás Nevinson meet in Madrid. Young and in love, they quickly decide to spend their lives together. While in England, Tomás is recruited by the secret service. He is unable to explain his long absences to Berta, and eventually disappears for good. Berta is left alone, in hopeless exile.
...a peculiar world, at once vague and precise ... Like most of Marías’s novels, Berta Isla revolves around ideas of what we know and do not want to know, of what we do not and cannot know, and the nuances and difficulties of communication. It makes many connections to his earlier works, especially Your Face Tomorrow. Like them, it takes place in a sort of epistemic haze. It is, if anything, more sinuous and satisfying than many of its precursors ... Berta Isla is often aware of its closeness to self-parody – the joking Oxford dons doubling up as spies, the slow, mannered prose and hurried sex, the seemingly endless musings and hesitations. But it is also full of humour and intelligence, and ranks as Marías’s best novel in years.
Marias takes a 19th-century approach to novel writing. He begins with the childhoods of Berta and Tomas and their first meeting at school in Madrid. He writes long, dense sentences that would please Henry James and require a similar level of concentration: though the payoff is a precision of nuance, the cost can be airless, claustrophobic prose. He is also given to sententious generalisation ...  s constructed from a handful of long conversations — between Berta and Tomas, Tomas and his Oxford tutor, Berta and other agents. These are thoughtful, intelligent examinations of the existential dilemma of the spy, but are unlikely as actual chats ... Under the pressure of all this cleverness, the novel feels abstracted, which is not helped by Tomas being so emotionally detached. This is perfect for a spy, but all the other characters are cold, too ... Berta Isla is a substantial, serious book about the human cost of being a secret agent, but it’s a peculiarly unsatisfactory novel.
This is not a novel about spycraft, the drama of going undercover, or even...the moral choices attending the profession of secret agent...Marías is above all interested in negative states: waiting, uncertainty, insignificance, ignorance, deception and self-deception ... Marías is...a remarkably long-winded writer who has made his prolixity a badge of honour. In the past, he has talked about using his writing to do a special kind of literary thinking, worrying at an idea over a succession of clauses to get at a kernel of truth or exactness. Yet on the page, this often comes across as fussy and distracting. The prose seems written more for its cadences than the images it evokes ... A man, or woman, who knew how to omit would release a much improved novella from this 544‑page tome. Interestingly, the slimmed-down book would be much closer to commercial than literary fiction ... perhaps the real master of deception is Marías himself, and his book is simply a potboiler in heavy disguise.