Hickman Gallery is a modern London gallery, run by Miss Wenceslas which appears as part of the fourth case (Alex Woodbridge part) in "The Great Game". The gallery has been greatly publicizing its acquisition of a lost Vermeer painting in the media.
After being called to a London crime scene containing the body of Alex Woodbridge, Sherlock deduces that he worked as a security for a gallery by his clothes and finds that the Hickman Gallery is the only one with a missing employee.
He deduces that this means that their newly acquired painting is a fake and that Alex somehow knew and therefore needed to be assassinated by an assassin called the Golem. He infiltrates the gallery, dressed as a security guard, to examine the painting.