A group of UK mercenaries operating in an eastern European country attack and kill a patrol of soldiers. Among them is a prisoner in white dress (Julia Szamalek) who initially appears to be a civilian. However her last words to Kia (Samantha Schnitzler) are a blood spat warning ‘don’t go down’, before Kia is forced to shot her by barking mad leader Stanton (Shayne Ward). Mission accomplished they return to the UK At the base the lift to the top isn’t working and so begin their ascent on foot.

On the trudge to the top there is what appears to be an explosion setting off alarms and the red emergency lights. Caught on the stairwell a member of the team goes down to investigate. His screams are heard and staggering back to the team he just says don’t go there as the viewers get a glimpse of what is happening, as the darkness ascends with the mercenaries within fate in it.

Forced now to move forward and away from the darkness, the team starts to fracture with some bringing up their religious beliefs to try to make sense of what is going on. The pressure builds and they crack leading to arguments and murder.

The survivors continue up the levels where they come across exits which transport them back in time to where possibly this all started and as the team gets smaller so they start to work out what as to be done and the sacrifices that have to be made.

Shot with a murky colour palate with the opening sequence and subsequent returns to the battlefield in a grey/blue hue The Ascent is not a great looking film what with the stark red of the lights in stairwell and green night vision goggle. But it does suit the overall tone of the film which is not that upbeat with scenes of atrocities and the team physically and mentally falling apart.

There’s a very superficial glance at Star Trek’s City on the Edge of Forever with its cause and effect of messing about with time. That was a tightly scripted episode while The Ascent, though not sloppy by any means, does begin to feel laboured though writer and director Tom Paton hasn’t fallen into the trap of over repeating the actions to get the desired outcome. Each of these sections are shot with enough variances to keep the interest.

Nevertheless it does feel a touch too long and the metaphysical discussions don’t add much depth to the story or the characters. The latter are sketchy though apart from the token mad commander don’t slip into cliché. Paton is on a something of prolific streak with a film a year since his debut Pandorica in 2016 followed by Redwood and Black Site. The Ascent is maybe not the strongest but well worth seeing.

The Ascent (known as “Black Ops” in the US) will be available exclusively on BirdBox.Film from 12 June and from 15 June - iTunes, Amazon, Sky Store, Sony, Xbox, Google Play