Arthur Conan Doyle’s pipe-smoking detective featured in four novels and 56 stories. In The Secret of Sherlock Holmes, recently on tour and now hastily booked into the Duchess Theatre to fill the hole left by the ill-fated The Fantasticks, Jeremy Paul adapts both all and none of them.

In the original 1988 production of this shortish two-hander, the part of Holmes was taken by Jeremy Brett, one of the great screen interpreters of the role. Here the deerstalker and Meerschaum are passed (or they would be if designer Simon Higlett had not dispensed with them in favour of drawing-room attire) to Peter Egan. He plays the famous occupant of 221b Baker Street with cuff-shooting, hand-on-hip panache and just a touch of stentorian camp, before descending into drug-addled derangement.

His Watson is Peter Daws, a stolid, dignified figure with a demeanour of middle-class Pooterism. The fact that he does not remove his tweed coat for the duration of the piece is an apt metaphor for the doctor's buttoned-up Victorian decency – although those buttons come under severe strain in one of the evening's most affecting scenes, when Watson blurts out how much he has missed the absent Holmes after his faked death on the Reichenbach Falls.

Equally deserving of plaudits is Higlett, who gives us a wonderfully cluttered, two-tiered Baker Street drawing room, with scarcely a hint of the Victorian railway platform or the Swiss torrent cunningly concealed within it. Revealing each of them is a simple but effective coup de theatre under Robin Herford’s direction.

The problem is the text, which eschews the central appeal of all the original stories – solving a good mystery – for a narrated ramble through the whole history of the Holmes/Watson partnership. There are some amusing moments, such as Watson lamenting that Holmes can recognise 42 different kinds of bicycle-tyre track but knows nothing about literature. But it’s fatally hampered by its aimlessness. Imagine a reworking of Agatha Christie, stitched from all the adventures of Poirot and Captain Hastings, with the murders themselves removed.

There is a mystery of sorts at the end, as Paul tacks his own coda onto the existing Holmes history to invent a new dimension to his epic battle with Professor Moriarty. It’s one of those twists that’s clearly meant to leave us reeling with its audacity. But it’s neither psychologically convincing nor dramatically sufficient to make up for the flimsiness of what has gone before.