Both Sherlock Holmes and Jack the Ripper inhabit a dark and sinister London in the popular imagination, full of cobbled streets and pea-soup smog, with danger lurking just outside the glow of every gas lamp. It was not until long after Sir Arthur Conan Doyle’s death that this fascinating if tasteless pairing was brought to fruition, resulting in two sharply contrasting films: “A Study in Terror” (1965) and “Murder by Decree” (1979).