Smiles on their faces and tongues firmly in their cheeks, the scarily talented Jeremy Legat and Ed MacArthur bound onto Gabriella Slade's marvellously detailed set in this fast-moving, affectionate homage to Agatha Christie.

Kinosian and Blair, who share writing honours (book and music Kinosian, book and lyrics Blair), obviously adore their source material and there's more than a dash of the Marx Brothers in Murder for Two. Much fun is to be had in moving the country house murder mystery from the traditional Brit stately home setting to the New England mansion of ace American crime writer Arthur Whitney. The surprise birthday party planned by his wife Dahlia gets off to a shaky start as a shot rings out in the dark. Is the killer one of the guests – or Dahlia herself? With the detective out of town, eager, likeable neighbourhood cop Marcus Moscowicz investigates.

The show's big coup is to have one guy (MacArthur) play the cop and the other (Legat) all the suspects. Both get to play piano, though necessarily, MacArthur's Moscowicz does more time at the keyboard. It's impossible to resist this pair. Some of the show's best moments are the gloriously precise transitions from piano to centre stage, topped by four hands on one keyboard. Legat morphs from one character to another by simply twisting a hat – or his features – and is equally at home as precocious boy chorister, fading southern belle Dahlia, seductive ballerina Barrette, scary psychiatrist Dr Griff – and all the rest of the 12 ill-assorted suspects. MacArthur is the perfect foil to all this frenetic activity and Luke Sheppard directs with pinpoint precision, so that every transition, every tiny movement is flawlessly slick.

Blair turns nifty lyrics that sit well on Kinosian's jaunty tunes, "every alibi must be cracked, when you're tracking your man just act – as protocol says". They probably imbibed Gilbert and Sullivan and Tom Lehrer with their mother's milk. Although it does become almost exhaustingly frenetic at times and the show is so knowing that it's hugging itself, there's much to love. And Legat and MacArthur certainly work hard to earn the love in the Watermill's intimate space. It should sit well in the studio when it transfers to The Other Palace. Meanwhile it makes for a delicious start to the Watermill's 50th anniversary year.

Murder for Two runs at The Watermill, Newbury until 25 February before transferring to The Other Palace from 2 to 18 March.