The Painkiller, Garrick Theatre

The fourth production in Branagh’s Garrick season is the revival of an odd-couple romp he brought to the Lyric, Belfast in 2011. Sean Foley (best known for his superlative Branagh-directed Morecambe and Wise tribute The Play What I Wrote) adapts and directs this nostalgic English version of Francis Veber’s 1969 French farce, which wastes no opportunity for dropped-trousers, door-slamming, mistaken-identity slapstick.

Branagh’s debonair hitman and Rob Brydon’s sad-sack Welsh photographer are in adjoining hotel rooms – the former commissioned to take out a witness testifying at the courthouse across the street, the latter trying to take his own life. Both plans go awry when their paths cross, with interjections from Brydon’s ex-wife (Claudie Blakley), her therapist/lover (Alex Macqueen), a policeman (Marcus Fraser) and a well-meaning porter (Mark Hadfield, pictured below with Branagh and Brydon) adding to the chaos.

The main selling point is Branagh and Brydon’s entertaining double act – the one menacingly contained, the other a babbling but endearing chump – and their vanity-free commitment. Brydon almost bares all in eye-wateringly skimpy pants and shows an equal emotional vulnerability, while Sir Ken endures multiple references to his thin lips and suffers a bewildering variety of medical side effects that leave him jelly-legged, staggering, wildly incoherent, momentarily discovering his inner Michael Jackson, and collapsing face first into a beanbag. If more studied than spontaneous, it’s still an impressive physical tour de force, particularly when his maladies are combined with furious attempts to inflict violence and/or conceal it.

The supporting cast has less to work with. Poor Fraser spends most of his professional debut hidden in a wardrobe, while Blakley (pictured below with Brydon), given mainly malapropisms and dubious class-based humour, does her best with a moment of semi-empowerment. Macqueen sells the transformation from supercilious shrink to red-faced rage monster, though a bout of amnesia gets lost in the shuffle. Hadfield fares best with his camp, increasingly desperate porter – mopping flood water by doing the twist with a pair of towels, absent-mindedly attacking his stress eczema, and all but shrieking his parting message: “Enjoy!”

Alice Power’s chintzy boutique hotel set produces the evening’s best sight gag via an overabundance of throw pillows, and the invisible wall between the rooms illustrates the illusory divisions between the two men. But Foley’s sometimes meandering 90-minute script causes confusion by mixing contemporary references with Seventies sitcom sensibilities. How to square “Netflix and chill” with the assumption that psychiatric care equals straightjackets and the mere suggestion of sex should leave us scandalised? Yes, this is a genre where the improbable is all but required, but if we cease to invest in the supposed life-and-death stakes, the slapstick loses its dangerous edge.

A late bout of introspection, which brings the action grinding to a halt, suggests an attempt at a deeper meaning – our need for human connection, even in a space as anonymous and isolated as a hotel – but can’t quite deliver in this cartoonish framework. Check in for the one-liners (impotence is memorably described as “like trying to get a marshmallow into a piggybank”), but if you’re looking for something more than goofy throwback, this hitman farce doesn’t quite hit the mark.

• The Painkiller at Garrick Theatre until 30 April

@mkmswain