It is 30 years since Holmes and Moriarty plunged together over the Reichenbach Falls. Sherlock, long since back from the dead, has retired to the West Sussex coast, enjoying quiet seclusion – until the dead body of his housekeeper is discovered on his private beach. Paranoia takes hold of the ageing sleuth as he begins to suspect his old rival might be seeking retribution from the grave or might have also survived the fall. Mary, wife of Dr Watson suddenly turns up to claim she has seen her long-lost dead son James through the window of 221B Baker Street where she resides with her estranged husband. Holmes is irresistibly drawn out of retirement and back on the track of a double mystery.

Simon Reade’s new play, set in the 1920s, introduces us to an older, retired Dr Watson, enjoying a sunset career broadcasting his recollections of his adventures with Sherlock Holmes over the fledgling BBC airwaves whilst freelancing as a psychoanalyst. Timothy Kightley plays a slightly bumbling but rather loveable Watson who is surprised but thrilled to be taking part in the younger generation’s tech revolution before an agitated Holmes bursts back into his life in true Conan Doyle style, still managing to shock the good doctor with his undiluted taste for class A drugs.

The play promises more than it delivers. While it dwells pleasingly on the asides, Watson’s broadcasts for instance, the Holmes brothers’ mildly abrasive relationship, or even on Miss Hudson’s banter as she dusts the mantelpiece, the nitty gritty of the plot trips up with an insistence that we believe some really quite silly scenarios – a séance that springs to life instantaneously for instance, and some clunky visual tricks that demand well-seasoned cynics in the audience suspend their disbelief unreasonably.

The most successful scene in the play had the least to do with the plot. Sherlock summons his brother for help, and they meet up on a park bench. Roy Sampson plays a wonderfully fading and fatalistic Mycroft Holmes while Robert Powell has at last got some emotional range to explore in an engaging duologue with his brother. Liza Goddard had little opportunity to explore the darkness of the character of Mary Watson before an extraordinary monologue towards the end which hinted at her victimhood. There was very good support from Lewis Collier as Detective Inspector Newman and Anna O’Grady, firstly as a prim BBC producer, then as chirpy housemaid Miss Hudson.

Jonathan Fensom’s set of the study in 221B Baker Street was lovingly adorned with detail – picture rails, fireplace and gas and electric lights. The sweep of a full curtain across the stage revealed new tableaux each time it passed, but it failed to reveal the level of excitement that would ­­have sustained a Conan Doyle original.    ★★★☆☆    Simon Bishop  at Bath Theatre Royal,  2nd May 2018