He returned to his legal career and was made a Queen's Counsel (QC) in 1964. "A master of courtroom theatre.. [whose] clashes with the Bench entered into legal legend", Platts-Mills was defence counsel to many clients, including the Great Train Robbers at their appeal and Ronnie Kray. Of the Kray Twins, who were found guilty of the murders of George Cornell and Jack McVitie in 1969, Platt-Mills later said: "I genuinely believed they were not guilty".