The reason for the profound anguish etched on faces from the outset of Reina's film soon becomes clear. As two teams enter the caves at separate points, looking to meet at the half way point, a blockage and momentary instance of panic sees two men lose their lives. Unable to retrieve them without putting themselves in mortal danger the remaining members of the crew are forced to abandon their colleagues in an icy grave. Recovery attempts by international experts fail. The local police outlaw diving in the area. Two months pass. Diving Into the Unknown then charts the underground - and illegal - operation to recover the corpses. With remarkable candour the hard questions are asked: At what stage of decomposition will they find the bodies? How can they prepare mentally for coming face to face with their fallen comrades?
It may sound extremely morbid but the practicality and determination those left alive demonstrate is incredibly uplifting. Where Reina's film really elevates itself beyond documentary norm is in an efficient inspection of the psychological devastation of this ordeal. The stoic reticence of men clearly traumatised, sleep-deprived and emotionally ruined by the knowledge of where their friends lay is deeply moving but tears and outward displays of emotion are kept firm-lipped. There's no sense of heroism, grand-standing or bravado either: they have a job to do and in order to move on with their lives - and to afford the loved ones of those lost the chance to grieve - they just have to get on with it. Upon returning to Plura, one in their midst is unable to go back in the water. His honest admission is not maligned, but instead respected as one lapse in concentration can have such dire consequences.
An ordnance survey map, cross-section showing the path of the caves underground and a depth gauge mark their progress as they plunge ever deeper. The photography - taken with GoPros - is astounding. At times it is impossible to see clearly in the murky darkness but this only amplifies the nail-biting dread of what awaits and every clink of an oxygen tank on cave wall is amplified ten fold through the body of water with chilling clarity. Diving Into the Unknown is riveting viewing. Take a deep breath and seek out this spellbinding work.
The 70th Edinburgh International Film Festival takes place from 15-26 June. For info visit edfilmfest.org.uk.
Matthew Anderson | @behind_theseens