The film is an account of the terrorist attack, on Patriots Day 2013, on the Boston Marathon perpetrated by the Tsarnaev brothers. It shows the carnage, especially the young couple who both had to have limbs amputated, how the bombers were identified and the bloody shoot out between the police and Tamerian Tsarnaev. The film implies that the brothers attacked the marathon out of the blue, having been radicalised. However the real story is that they had been suspected of criminal offences and radicalisation for years. The Russian government warned the US about the family’s behaviour on two occasions. Tamerlan remains connected to a triple homicide in Massachusetts in 2011. So what did the security services really know?