At the crack of dawn in residential Newcastle, a man is violently assaulted and stabbed in his home by two unknown assailants. The suspects flee the scene and it is the job of rookie CSI Nicola Stark to examine the crime scene and surrounding area to find the clues that could lead her to identify the attackers. In Sunderland, a woman reports being raped by two unknown men in a block of flats. Intimate samples are immediately taken as these provide the best chance of identifying the unknown suspects and bringing them to justice. But with two different, and as yet unknown people’s DNA present in the samples, identifying individual DNA profiles for comparison with the national DNA database is no simple matter.