A Sherlock Carol is what young folk describe as a mash up – a cunning melding of elements from Conan Doyle and Dickens to produce something totally unexpected that is both funny and clever.

In writer-direcetor Mark Shanahan's witty, festive play, a dishevelled Sherlock (played with insight, depth and a sense of the absurd by the excellent Ben Caplan) is having an existential crisis.

Three years on from the death of Moriarty at the Reichenbach Falls, he wonders what he is for: “There is no use for Sherlock Holmes if Moriarty is dead.”This Is Local London: Ben Kaplan and Richard James in A Sherlock CarolBen Kaplan and Richard James in A Sherlock Carol (Image: Danny Kaan)

Morose, self-critical and confused, the great Detective is losing friends and respect, and the Holmes/Watson team is no more. Wandering the foggy streets of London, he is recognised by (now Doctor) Tim Cratchit who asks for help. His benefactor Scrooge has been found dead and the murderer must be found. Initially Holmes refuses, then announces: “The game’s afoot!”

The two hours that follow are a spirited, wonderfully enjoyable concoction of waifs, talking door knockers, tampered-with geese, hauntings and dreadful cockney accents.

There is an abundance of puns, nudges and theft from both canons to keep the most avid Dickens and Conan Doyle enthusiasts happily on their toes. It's far from slapstick: Sherlock's creator would have been proud of the deductive reasoning that leads to the unveiling of the victim.This Is Local London: Kammy Darweish in A Sherlock CarolKammy Darweish in A Sherlock Carol (Image: Danny Kaan)

There are also a few carols, a dose of redemption, and a Dickensian festive message: Be Nice! All members of the small cast are exceptional - not least the comically talented Richard James (Dr Watson and others). Their enthusiasm for the play shines through – in this case a happy cast makes for a happy audience.

A Sherlock Carol is the first Christmas show hosted by the brand-new Marylebone Theatre - a stones' throw from the fictional 221B Baker Street. Big enough to be a “proper” theatre and small enough to be intimate, it's well worth getting on the mailing list to see if they can keep up this standard.

A Sherlock Carol runs at Marylebone Theatre, Rudolf Steiner House, Park Road, NW1 until January 7.https://www.marylebonetheatre.com/productions/a-sherlock-carol