3x10 - Murder Call

Tessa and Steve uncover a web of intrigue surrounding businessman Brian Hart's horrific death when he is killed as he commutes to work by train when a letter bomb concealed in a card explodes. Tessa and Steve are confronted by a bewildering array of suspects and motives to finally apprehend the person they believe to be the killer, only to realise at the last moment that they only have it half right.