There are difficulties in adapting for the stage three of the four Sherlock Holmes stories, including this The Sign of Four, since as novels they have a quite a primitive structure. Each runs a dual narrative; one by DR Watson, the faithful Holmesian sidekick, as he painstakingly outlines crime and investigation, and the other is a story told by an omniscient narrator of events leading up to the crime and set in an exotic locale; here India at the time of the Mutiny. The adapter must decide how to integrate the two strands, how to cross-cut between them, what to do with the literary nature of the Watson narrative, and what to omit in the interests of a, say, two-hour running time and the requirements of dramatic spectacle.

Director and adapter Nick Lane has chosen to retain Watson's narrative voice, I imagine in order to honour an essential part of the original authorial method. But his drama is top-heavy with plodding slabs of exposition and light on scenes of action and movement. The explanation by Jonathan Small, the thief brought to book by Holmes' investigative powers, which essentially concludes the play, ends up being over-detailed to the point of confusion, and also too prolonged.

The action scenes which are included vary in their effectiveness. We had a stylised fight between Holmes and an ex-prizefighter which seemed to serve the purpose principally of breaking up the cascading descriptive talk all around it, and it was oddly performed in slow-motion. A hansom cab ride through London was quite well done, and later a boat chase down the Thames was simply but well staged by means of stage props and body language, but then went on a little too long. There were also strange omissions: time was spent on Holmes examining a body and making inferences from it, but no body lay on the floor. Tonga, the dwarfish Andaman Islander who assists Small in his greedy enterprise in London, was much referred to but failed to appear. The police Inspector Athelney Jones was turned by the script into something from vaudeville, a pure clown with his tedious insistence of getting Watson's name wrong and his blundering (and I blinked at his anachronistic: 'well, there we go!').

Our six actors, all taking more than one part and four of them multi-roles, doubled as musicians, lurking at the back and occasionally venturing onto stage. Thus Miss Morston (Stephanie Rutherford) was also seen on trombone and later played the fiddle. Thaddeus Sholto (Ru Hamilton) played a nice sax and clarinet, and so on. In that role, I thought Hamilton and also Joseph Derrington throughout as a sturdy Dr Watson were the pick of the actors, though Zach Lee's Small was sinewy and quite powerful. Rutherford had an unvaryingly loud, harsh voice which was off-putting, and Luke Barton I thought a weak Holmes, looking too young and fresh-faced, and vocally bland. Nothing of the incisive brain, cutting through the impossible to get at what may be improbable but the truth.

But let me single out Victoria Spearing's terrific set. This was in Indian mahogany, an elaborate confection of strong verticals topped by minaret-type pinnacles and pyramidal roofs, cris-crossed by a mathematical maze of wooden rails and struts. Backed by tall brilliantly lit strips of crimson curtain, it was preceded by a floor of black and white intricate Moorish design. The set was constantly being broken up and employed for the succeeding scenes in ingenious ways. The opening effect of set and Indian music including the sound of a tamboura was just magical.