What is the cost of keeping a secret from someone you love? In Berta Isla, a novel by the celebrated Spanish author Javier Marías, a couple’s minor disloyalties – which they justify as mere ‘parentheses’ or emergency measures in their relationship – breed further betrayals until they find their lives ‘swathed in mist and mystery’. When does an extended parenthesis overwhelm the sentence in which it occurs? How long can you lead a parallel life before it supplants your real one? At what point does a state of emergency become, simply, the law? These questions all bear upon the action of this guileful and beguiling tale. Like its characters, Berta Isla is a shape-shifter: part spy thriller, part murder mystery, part cerebral caper with echoes of Melville, T S Eliot and Henry V. It is also a trans-European historical novel, set between Oxford and Madrid in the 1970s and 1980s, with a hinterland that includes the campaigns of ETA and the IRA, the fall of Franco, the rise of Thatcher and the Falklands War.

But at its centre is an anxious, brooding domestic drama. Classmates Berta Isla and Tomás Nevinson are not yet fifteen when they fall in love, knowing at once ‘that theirs was a serious relationship and not a brief flirtation that would end along with the term’. Berta, a ‘dark-haired