Ideally there would be a town crier outside every screening of Ma Ma, bell ringing to warn the paying public: "Pet project!… Pet project!" Julio Medem, best known for his sexfests Sex & Lucia and Room In Rome, might be the writer-director but with Penelope Cruz producing and starring methinks the actress was involved every step of the way. With all pet projects there's a danger that those involved are too close to the material to notice the wobbly bits. And Ma Ma has wobbly bits.

Cruz is Magda, a single mother diagnosed with breast cancer. The day she receives the bad news is the same her teenage son Dani (Planell) is offered a trial with Real Madrid by junior scout Arturo (Tosar). However, no sooner does Arturo offer Dani his chance he learns that his daughter has been killed in a hit-and-run and his wife is in a coma. United by their respective tragedies, and by their shared interest in Dani’s future, Magda and Arturo's friendship graduates to love. But there’s more bad news in store for Magda…

The synopsis has to stop there because there's no real moment that launches the story - it keeps developing, heaping new woes and unexpected turns right up until the final scene. It makes overtures to be a certain kind of film, but then swerves into something else before thinking again and deciding on another route. At first it looks like finding the good in life during our short time left - initially a football hater, she tunes into Spain's run at Euro 2012 but enjoys the joy it brings her neighbours more than the game, watching the celebrations in the apartments opposite with her back to the actual game on TV - but this peters out. Then it’s about finding love again with Arturo but that has zero drama, despite Magda confessing to her doctor, Julian (Exteandia), that Arturo suffers from erectile dysfunction.

Exteandia's Julian is problematic too, always threatening to play a bigger role in Magda's life but never does. Inexplicably emotionally invested in his patient, the story makes inroads into his private life and his thoughts about adopting a ten-year-old girl from Siberia. That girl, Natasha (Anna Jiminez), whose slow, eerie walk across the Siberian wilderness opens the film, also looks like she’s going to be a major development but is too sidelined.

There are other bizarre decisions afoot. Why Medem chooses to place the camera where he does in some scenes (above the door in Exteandia’s office) is anyone's guess. Why does Exteandia sing her a lullaby before surgery? Why does Exteandia turn up on Magda's holiday and extol the virtues of Magda during the resort's karaoke night? The melodramatic weepie music won't leave things well alone either. And there was one perfect moment to end the story but Medem can’t help but include an indulgent epilogue.

But Cruz is on form and despite the narrative's shortcomings there’s just enough unpredictability to keep one guessing.