At the clowning climax of The School for Scandal, the first production of Bath Theatre Royal’s summer season, a devious aristocrat feverishly skits around the stage in an attempt to keep the woman he has been impertinently flirting with hidden behind a screen from her husband and his brother. In Terry Johnson’s Hysteria, the second play of the season, a very similar scene occurs – this time it’s an aged Sigmund Freud concealing a nude and unstable critic of his work from his doctor, Yahuda, and Salvador Dali. Naturally.

The difference is that the high farce of Scandal’s screen scene is the explicable crest of Sheridan’s comedic wave; in Johnson’s play the comedy is just one element of a curious dramatic synthesis that takes in mystery, madness and melodrama in equal measures. There’s no doubt this makes for an intriguing evening – starting with the arrival of perturbed student Jessica, the addition of each new character to the dialectical melting pot of Freud’s Hampstead study (beautifully designed by Lez Brotherston) allows for greater complexity in the play’s discussion of questions concerning psychological ethics and Jewish identity, as well as greater mayhem in the many moments of levity. But though there is skill to the deftness of touch with which Johnson – as both writer and director – moves between such scenes, he struggles to achieve overall cohesion; the complete impression is rather hodgepodge, or, if you will, surreal.

Considering the centrality of Dali to the play – the second act climaxes with a glittering visual coup de théâtre ripped straight from one of the Spaniard’s canvases – this frenetic clash of the realist and the ridiculous may well be the point. Even so, it leads to moments where the characterisations of these real-life personas are questionable, and where the momentum of the broader narrative is arbitrarily halted, for a lewd sight gag or cheap sex joke. In Orton’s What the Butler Saw, farce is used as a vehicle to explore the insanity of insanity; here, by the time we come to the crux of the piece – an interrogation of whether Freud’s 1897 theory of infantile sexuality came about through opportunism and self-deception – the connection between form and content has come under strain.

For the most part, this is a strain which does not inhibit the performances of the cast, led by a sensitively restrained Antony Sher, who, in the measured conviction of his voice and the weary slump of his head, captures Freud as a man whose intellect continues to burn bright even as his body succumbs to an aggressively cancerous jaw. His is also perhaps the most admirable technique for getting laughs from the audience – unlike the outrageously mannered Will Keen as a caricaturish Dali, he never plays for them. Indira Varma may have taken a little too much inspiration from the title of the play in shaping her performance as Jessica, but becomes more genuinely affecting as the evening progresses and her real motivations for visiting Freud and questioning the basis of his theories becomes clear.

Structurally flawed as it is, Hysteria remains remarkable among the glut of farces which have emerged onto the theatrical scene in the last year, for deriving its power not from the crotch and the stumble, but from the head and from history. Rarely riotously funny, Johsnon has nevertheless put something on the Bath stage which strikes a balance between entertainment and incisiveness that many a more conventional playwright would do well to aspire to.

Hysteria plays at the Theatre Royal Bath from 26 July-18 August 2012. For more information, visit their website.