Charles Marowitz’s Sherlock’s Last Case comes wreathed in many mysteries, not the least of which is why a play of such marvellous entertainment value, concerning a great fictional detective known to all, is so rarely staged.

The cuttings library at The Oxford Times contains but one review of the piece, and that dating from as long ago as 1980. At that time the play was still presented as the work of Matthew Lang, under which assumed name Marowitz had knocked off the 90-minute one-acter in a matter of days in 1974 to fill a gap in the schedule of London’s Open Space Theatre, which he had set up with producer Thelma Holt.

It was not until the mid-1980s, when Marowitz was back in his native US, that he owned up to authorship as he refashioned the play into two acts for a Broadway production starring Frank Langella (famed as a screen Dracula) as the omniscient Holmes.

That the sleuth was omniscient, never one to be worsted, has proved to be — along with his know-all nature and insufferable arrogance — among his most tiresome characteristics. With a cheery insouciance he tells Dr Watson here: “A day without a threat to my life is like a jour without soleil.”

As supplied by Marowitz the words throughout the play are strung together with an aphoristic expertise almost to rival that of Sir Arthur Conan Doyle. The crisp and mannered delivery of Christopher Godwin, an actor of rich and wide experience, presents them with an authenticity that will be savoured by every Holmesian, all but the most hidebound of whom will relish the gentle mockery of their hero and the absurdity of the situations into which he and sidekick Watson (the excellent Adam Kotz) are drawn.

The mainspring of the plot is the arrival at 221B Baker Street of a letter purporting to come from one Ralph Moriarty, the previously unknown son of the villainous Professor Moriarty, who was killed (as Holmes also was and then wasn’t) in the momentous confrontation between good and evil at the Reichenbach Falls.

Vengeance is his ambition, and once the garrulous Scottish housekeeper Mrs Hudson (Alexandra Mathie) has been tricked northwards, the game — as Holmes would put it — is on.

Despite the efforts of another Moriarty child, Liza (Victoria Grove) to defuse the situation, simultaneously charming the usually female-resistant Holmes, the unseen Ralph soon looks to be doing his worst.

Knockings from a cupboard lead to the discovery of the bound and gagged Dr Watson. Further serious unpleasantness follows as designer Simon Kenny’s splendidly atmospheric set transforms to admit us to a dimly lit cellar which quickly becomes a torture chamber for Holmes.

Will he survive this encounter with villainy? Will the forces of law as represented by Insp. Lestrade (Alister Cameron) help him to sleuth another day? The play, expertly directed by Maria Aitken, grips us to the end.

By then we have finally come to meet the mysterious Ralph - and quite a character he proves as presented by Roger Covivati in an impressive professional debut.

Seen (or rather not) during his student days at the Guildhall as HG Wells's Invisible Man, Roger is a young actor one might hope to see much more of in the future.

Godot would be an appropriate role for his very special talents.