Gordon Corera investigates the mysterious illness that has struck American diplomats and spies. It began after some reported hearing strange sounds in Havana 2016, but reports have since spread around the world. Doctors, scientists, intelligence agents and government officials have all been trying to find out what exactly causes these sounds and the lingering health effects. Some call it an act of war, others wonder if it is some new and secret form of surveillance while others believe it could even be in the mind. So who or what is responsible?