Our first case concerns a young man, Dolton Powell, fatally stabbed by an armed gang after a party. A group of suspects are arrested and questioned, but they remain tight-lipped and give nothing away to investigators. In a bid to uncover the truth about the horrific crime, police secretly record the young men as they huddle together and discuss the events of the night. However, they speak in a secret language that was hard to understand. They needed expert help and turned to forensic linguist Nicci MacLeod, who had to crack their code, decipher the true meaning of what they were saying and eventually prove their guilt. With powerful testimony from Dolton's sister Andrea who recalls the devastation the gang caused and a step-by-step account of the case from investigating officer Sophie Ferguson. Expert witnesses can help solve all types of crime - not just violent ones. In the second investigation in this programme, police received reports about suspicious activity at a business premises in Kent and discovered a large-scale cannabis farm run by an organised crime gang. Detectives soon realised that this particular site was a drop in the ocean, and the drug traffickers were in fact running a country-wide operation. However, to bring about charges, they needed to know exactly how much of the illegal drug this huge factory could churn out, so they called on the help of drug expert Adrian Parsons to calculate the financial value of the cannabis the gang were producing. His evidence helped convict the gang, and their custodial sentences totalled over 90 years. It was one of the biggest cannabis operations ever discovered in the UK.