In writing a romantic musical about consuming love, Stephen Sondheim wrote a show that is hard to like. The music is flat and uninspired for long stretches, almost shockingly banal at the start, and not really redeemed by some good anthems and chorales towards the end.

I’m sorry, I only want to hear one person sing a song with “happiness” in the title, and that’s Ken Dodd. But with one weak link in the casting, Jamie Lloyd’s exquisitely arranged revival – less hysterical and less overblown than the 1996 London premiere with Maria Friedman and Michael Ball – makes the best possible case for a second look.

Both married lover Clara (Scarlett Strallen) and deformed invalid Fosca (Elena Roger) have Giorgio on their minds. He’s an Italian soldier diverted from a sunlit dalliance by a posting in a remote garrison; and Fosca, like Tosca, pines and perishes on the ramparts.

Roger is radiant even when supposedly hideous. Strallen sings her letters, sometimes invading the soldiers’ table in the outpost, and basks in perennial happiness until she realizes there’s another woman. Giorgio is sung with sterling bravura by David Thaxton, but his acting is full of face-pulls, and there’s no coherent emotional signal.

James Lapine’s book is adapted from an 1869 novel and a 1981 movie, both Italian. The subject is not really Sondheim’s style, and he doesn’t do Rodgers and Hammerstein, or Puccini, as well as Andrew Lloyd Webber does.

Christoper Oram’s design of frisky frescoes and green doors, Neil Austin’s beautiful lighting and Alan Williams’ musical direction are all well up to Donmar scratch. Lloyd’s company move smartly on and off, bearing furniture, like a bunch of singing removal men; there are some lovely chiaroscuro effects with raised glasses and candlelight. Passion was under-heated first time round, and it’s still cooling.