Neighbours heard the murder, heard the victim calling out for help. As one of them rushed to help, he found the victim, Dr. Richard Castillo, falling to the ground by the entrance to 3 Albert Bridge, Battersea, mortally wounded by two deep stab wounds. But the killer had vanished.

Dr. Castillo, a 70-year-old Maltese GP, had been called to the address by the Thames in south-west London, at 11.20 one Saturday night. When he hadn’t returned by 1.30 a.m. on the Sunday, May 7th, 1961, his daughter called one of his partners, who told her that they had no patients in the Albert Bridge area. She phoned the police, who discovered that the house had been vacated on the morning of the murder – a fact that must have been known to the killer.

Who was he? Even more puzzling, what was his motive?