Explosives officer Lana Washington and her team are called to investigate a suspected bomb in a black cab that has been abandoned on waste ground, but they soon realise they're at the site of something far more sinister. Working alongside their colleagues in counter-terrorism, the team races to find out what the person behind this unique bombing campaign wants, who they are and who they might be targeting next.

With two incidents appearing to be connected, counter-terrorism police work to establish a link between the two victims - a retiree and a university lecturer. As the investigation continues, Lana and the team grow suspicious that they aren't being told the whole truth, and an intervention from DS Helen Morgan backfires, leaving the unit at a loss.