Psychological thrillers — or ‘thrillers’ as they used to be known — have become almost as ubiquitous on television as they are in the average bookshop. On the whole, this is now a genre where contented domesticity exists solely to be undermined, and where the chief function of the past is to come back and haunt people — which is clearly what it’s going to do in Channel 4’s Born to Kill, even if Thursday’s increasingly intriguing first episode was in no hurry to explain exactly how.