Bell Pottinger, Britain’s most audacious public relations firm, always seemed defiantly beyond shame. During its 30 years in the upper echelons of Britain’s spin doctoring game, it sought to polish the image of dictators, repressive regimes and celebrities accused of despicable crimes (the Olympic runner Oscar Pistorius after he was charged with murder). But in 2016, Bell Pottinger signed a client that ultimately buried it in disgrace.