This is the hunt for a people smuggler, codenamed Scorpion, one of the central characters controlling the transport of migrants from the European mainland into the UK. It is a tense and disturbing investigation, recorded as it happened, in real time.

Barzan Majeed - codenamed Scorpion - leads the Scorpion gang. He's on international most-wanted lists. He started his criminal career in Britain and went on to build a smuggling empire which now spans the globe.

An international police surveillance operation trapped more than 20 of his gang and almost netted Scorpion himself, but he was tipped off and escaped. BBC journalist Sue Mitchell, and former soldier and aid worker, Rob Lawrie, team up to try to do what the police have been unable to achieve: to find Scorpion, to speak to him, to ask him to account for his crimes and to seek justice for those families he has harmed.

Their investigation takes them to the heart of an organised criminal gang making millions from transporting thousands of migrants on boat and lorry crossings that in some cases have gone dangerously wrong, causing serious injury and putting lives at risk. They witness his operation in action and record as intense situations unfold, where vulnerable people desperate for a better future, put their lives in the hands of ruthless and dangerous criminals.

As they edge ever closer they meet the people helping and supporting Scorpion, they unpick the financial side of his business funding his luxury life, they start to understand the man himself and to garner enough clues to trace his whereabouts.

To Catch a Scorpion is a BBC Studios Audio Production for BBC Radio 4 and is presented and recorded by Sue Mitchell and Rob Lawrie.