This is a truly underworld excursion. With its dark aesthetic we feel totally submerged, almost underwater and certainly cut off from any elements of ‘known’ life. Hence the impact on the viewer of its riff of identity transference and shifting personas as the agents go undercover. Because it is so all-consuming we respond almost as viscerally as its protagonists do, making the shocks that come – and their psychological violence – felt, rather than merely seen. — Roger Westcombe