Over the past few years, a reclusive Italian writer has sparked an international media frenzy with her irresistibly absorbing Neapolitan novels, My Brilliant Friend, The Story of a New Name, Those Who Leave and Those Who Stay and The Story of the Lost Child. Elena Ferrante caused a publishing sensation – without revealing her true identity behind the writer's name.

The best-selling books captivated a world-wide readership, who became lost in Ferrante's vivid descriptions of trust, tension and devotion between heroines Elena (Lenù) and Raffaella (Lila).

Now Ferrante fever returns with a two-part stage version of the saga, adapted from the novels by playwright April De Angelis (Jumpy 2012, After Electra 2014).

The tale, for the unfamiliar, is narrated by Lenù and follows her life and that of her friend Lila from their 1950s childhood deep into adulthood, as they struggle to escape the confines of their working-class upbringing in a deprived district of Naples. This is a Bildungsroman of epic proportions, one which tracks the complicated relationship between the friends over 60 years as they succeed and falter in their lives while battling male oppression, the rigid class system, gang intrigue and the changing social landscape of post-war Italy.

De Angelis condenses all five novels (around 1,600 pages) into a double bill stretching over some five hours. (To get an idea of how demanding this is, just consider that an Italian production company is about to make a 32-part TV series of the novels).

Part one consists of the first two novels in the series, My Brilliant Friend and The Story of a New Name. Punctuated by interludes of Purcell's Dido and Aeneas, it tells of the friendship of Lenù (Niamh Cusack) and Lila (Catherine McCormack) from childhood, in the context of their difficult, adverse circumstances.

In the novels we learn about our narrator, Lenù, through her recollections of Lila. Unfortunately, this is lost in the adaptation, and narrative depth disappears along with it. It's unhelpful that the scenes are often over far too soon to meaningfully establish the relationship; it seems as if the audience is informed of the ins and outs of the friendship, rather than seeing it unfold.

The play is, at times, fairly baffling. Initially, Cusack and McCormack are portraying Lenù and Lila as children, and not the middle-aged women they later become. And there is an enormous amount of doubling up, with the cast taking on several parts each (there are 32 characters to a cast of 12). Without some prior knowledge of the novels, the play is in danger of losing coherence.

Visually the transition from page to stage is sleek. Acts of violence take place against clothing, which represents the physical being of the characters, and one scene, at the seaside, is evocatively played out with sheets tumbling across the stage to emulate waves. And Soutra Gilmour's set design goes some way towards conveying the feel of mid-20th-century Naples, with its rusted balustrades and tall balconies.

For part two we leave Purcell for Jimi Hendrix and Cyndi Lauper, to demonstrate changing tides. The titles of the next instalments – Those Who Leave and Those Who Stay and The Story of the Lost Child – slightly give the game away; tragedy is a staple of this part of the tale.

Again, the stage adaptation suffers from brevity. Where we could fully inhabit Ferrante's prose, on stage we must rush through the stories.

It is, on the other hand, easier to accept Lenù and Lila in adulthood from the outset, and the development of both women is fascinating. Across the five hours Cusack inhabits Lenù with a moving bashfulness which grows into confidence, yet which always remains somewhat fragile. McCormack's Lila is her caustic, powerful antithesis.

Though My Brilliant Friend on stage doesn't shine quite like Ferrante's prose, it has enough theatrical flair to work as production in its own right.