This week Will tells Josh about Gareth Williams. A Welsh mathematician and employee of GCHQ seconded to the Secret Intelligence Service (SIS or MI6) who was found dead in suspicious circumstances at a Security Service safe house flat in Pimlico, London, in a duffel bag, in the bath, naked. Was it KGB? Was it an inside job? Or a magic trick gone horribly wrong, or a sex game gone horribly right?