Vargas Llosa defined the writer's work as

two things at once: a reconstruction of reality and a testimony to the dissent (of the writer) from the world.
Indissolubly united, these two ingredients will appear in the (writer's) work, one objective and the other subjective: the reality with which (the writer) finds himself at odds and the reasons for this enmity; life as it is and what he would like to suppress, add, or correct in life

.
Outwardly, the novel expresses precisely this conflict.
In the odd chapters unfolds the story of an eighteen-year-old who dreams of becoming a writer and who, in 1950s Lima, falls in love with his aunt—Aunt Julia, to be precise.
Family relations (grandparents, countless aunts and uncles, cousins), the working environment of the radio station, dive bars and disreputable neighborhoods, Peruvian villages—all form the backdrop for a lively and engaging narrative, yet one that is essentially conventional, leading as it inevitably does to falling in love and the complications bound to afflict a romance between a minor and a much older woman.
In the even chapters, by contrast, a writer of radio serials (the scriptwriter) invents incredible, marvelous, and catastrophic tales: entirely fantastical stories, which are without doubt the most captivating part of the novel.
The trouble is that imagination runs away with him: the scriptwriter can no longer govern his own stories and, above all, his own characters.
One day, the scriptwriter confesses to the aspiring writer that

something embarrassing is happening, I don't remember the scripts very well, I have doubts and slip-ups occur

The characters "get mixed up."

When I realize it, it's too late.
You have to perform acrobatics to put them back in their places, to explain their transformations

.
With exceptional mastery, chapter by chapter Vargas Llosa injects into each story broadcast over the airwaves ever-increasing elements of confusion, building toward a pyrotechnic finale.

Yet is this conflict between odd chapters (the realistic ones) and even chapters (the imagined ones) truly genuine? The young eighteen-year-old’s story begins like a classic nineteenth-century novel, but it too subsequently loses itself in improbable events—one need only consider the two lovers' wanderings through the Peruvian countryside in search of a mayor willing to marry them.
And when, many years later, the young writer—now established in Europe—returns to Peru, he discovers that the vicissitudes of life mirror the fate of old radio scripts:

the humidity had effaced the lettering, mice and cockroaches had nibbled and shat upon the pages, and the scripts had become intermingled with one another.
There is no way to choose: at best, one can try to discover some legible text.

Was the scriptwriter right, then, when in his delirium he declared:

what is realism, gentlemen, what is this much-vaunted realism?

The interweaving of imagination and reality (the true guiding thread of the book) is achieved not so much through the narrative structure (rich in characters and episodes though it may be) as it is rooted in a language and syntax that marvelously fashion a sense of evanescence and fantastical suspension.
Consider the opening of the twelfth chapter, undoubtedly one of the finest:

in the dusty center of the city, halfway down the jiron Ica, there is an old house with balconies and shutters whose walls, mottled by time and uncouth passersby (sentimental hands carving arrows and hearts and scribbling women's names, perverse fingers sculpting genitalia and swear words), still allow one to glimpse, as if from afar, faint veils of what had been the original paint, that color which in the Colony adorned aristocratic residences: indigo."

Why read it? It is a wonderful book that reads in a single breath, an escape from reality.
It is the work of a truly great writer.

Aunt Julia and the Scriptwriter