You have to give credit to director/producer Guillermo del Toro for supporting the darker material, particularly those with a European flavour like 2007's The Orphanage and this second feature from director Guillem Morales, both of which he produced.

Heavily influenced by the likes of Hitchcock, Morales takes his heroine on a journey into fear and darkness.

It's not just a natural bond that Julia shares with her twin sister Sara (both played by Belén Rueda); she also shares a degenerative disease that effects her eyesight. For Sara, being plunged into a world of darkness was just too much, so she took her own life.

Julia not only has to cope with the loss of her sister, but also the loss of her own sight, which is getting worse with every episode that she has.

Despite evidence proving otherwise, Julia just can't accept that her sister would commit suicide. Her notion that her death was caused by foul play is re-enforced when she discovers that Sara was 'seeing' a mysterious man.

Julia then decides to do some detective work of her own, but for everyone who knew that she was seeing someone, no-one can actually remember what he looks like, as if he were almost invisible.

With further probing, Julia delves deeper into truly dark territory; not only does her sister's case become ever more suspicious, Julia's loss of vision becomes more prevalent.

Thank god you're here. I've never seen a spider THAT size before - kill it!

Morales pulls out a lot of visual trickery to give the film a tantalisingly tense experience. He's clearly a fan of Hitchcock, borrowing as he does quite heavily from the master of suspense. Possibly too much in places, particularly elements from Rear Window. Still, it looks the business.

Where it trips up however is with the script. The story simply becomes implausible in places, far too frequently. You can only ask an audience to suspend belief for so long, otherwise the suspension snaps and an audience is left scratching its head.

For instance, would a doctor really allow a patient, who is currently blind, to go home and recuperate on their own after major surgery? Only if they wanted to be struck off soon after. There's also a minor sub-plot that reveals that Julia's husband was actually having an affair with her twin sister. It's the kind of story that would have Jeremy Kyle foaming at the mouth at, but oddly here it's kind of greeted with subdued acceptance. Maybe it's just a Spanish thing.

It's a shame that the story just doesn't add up, because Morales shows a real technical gift for setting up a scene that can have you on the very edge of your seat.