Marguerite, Theatre Royal Haymarket, London

Alain Boublil and Claude-Michel Schönberg, the creators of Les Miserables, like to set love stories against vast political backdrops. In Miss Saigon they transplanted a Madam Butterfly-style relationship to the Vietnam War. And now, in Marguerite, the new musical for which they have written the book, they have updated La Dame aux Camelias – the inspiration for Verdi's La Traviata – to Paris during the Nazi occupation.

The Marguerite Gautier-figure is traditionally a consumptive courtesan who nobly agrees to renounce her young lover, at his father's behest, to protect the family name and to safeguard his future.

The political stakes in that gesture of self-sacrifice are powerfully raised in this (by and large) intelligent and absorbing adaptation. Ruthie Henshall's Marguerite is a Parisian chanteuse with a past, painfully caught between her role as the mistress of Otto, a German officer, and her secret affair with a young pianist who has friends in the Resistance.

Jonathan Kent's fluent, strikingly designed production opens and ends with the liberation of France and the shocking spectacle of the heroine being attacked by an angry crowd who spit at her and hack off her hair. Then in a swift, savagely ironic flashback to her 40th birthday party in a swanky mirrored room, the assailants are revealed to be the very toffs and racist collaborators who were only too happy to lionise her and to take advantage of the luxuries (petrol coupons and silk stockings) that came with her high-ranking German connections.

The lovely score is by French composer, Michel Legrand, but, given the subject matter, it's no surprise that they have chosen to premiere the piece in London rather than Paris. Sung by a chorus of city-dwellers, there's a number called "Day By Day" that recurs through the drama and registers, in tripping measures, the fickleness and opportunism of these folk as political fortunes change – from the smugness of "All the heydays/ All the paydays/ Like before" to the apprehension of "There is a lesson to learn/ Always be ready to turn".

According to the louche nightclub singer who performs at a decadent New Year's Eve thrash, Paris is an amoral survivor: "Forged in revolutions lost and won/ She will still be Paris when we're gone".

The music is full of those undulating, never-ending, minor-key-seeking melodies that are the trademark of the composer who penned such hypnotic tunes as "The Windmills of Your Mind" and "The Summer Knows".

Ruthie Henshall's worldly but vulnerable Marguerite is in ravishing voice. She eschews standard-issue belting and is all the more moving for the delicacy and range of colour of her delivery. And I have rarely heard singing of such ardent, youthful rapture as that which pours from the ridiculously talented and handsome Julian Ovenden, who, as Armand, also plays a mean jazz piano.

With Armand's resistance-worker sister at his mercy, Alexander Hanson's emotionally frustrated German officer forces Marguerite to write a letter of renunciation to her lover, and Henshall is heartbreaking as she sings a secret denial of her words between the callous dictated lines.

But in the second half, the drawbacks to the update become harder to ignore. In plot terms, we see how the love affair places Armand's idealistic friends in grave danger and it's true there are sequences where overlapping duets contrast the hermetic, inward-looking nature of the romance with the risk-ridden world outside.

Musically and dramatically, though, the emphasis invites us to accept the affair at the lovers' valuation and this is a strain, given the broad context. It sentimentalises Marguerite to present her as a victim who had little choice in shacking up with a German. And it feels like a fudge not to acknowledge that in assassinating Otto, Armand exposes her to the humiliation of her fair-weather friends. Still, this is a compelling, if flawed, new work.

To 1 November (0870 901 3356)