When Sergei and Yulia Skripal were poisoned with a nerve agent, police faced one of the most complex investigations in their history. They had to trace a weapon which they could neither see nor smell, but it could kill thousands. In this episode, we hear how they checked everything from coins to...

When Dawn Sturgess and Charlie Rowley were taken to hospital, the emergency services tried to piece together what had happened to them. We hear how they questioned whether it was a coincidence that they had treated two people for nerve agent poisoning four months earlier or whether the events...