The light of an open doorway beckons through the mist of a London Particular, one of those smothering fogs for which turn-of-the-century London was famous. But in realityas Sherlock Holmes soon discoversthough the doorway does indeed offer respite from the fog, it also leads to the gruesome remains of a double-murder. Two corpses, a stolen diamond necklace, a Russian connection, and a dandified American writer who pals around with denizens of the theaterall add up to a murder investigation with international implications. Leave it to Sherlock Holmes who, in a classic assemblage of suspects in a high-tone British mens club, employs