Kitty agrees to this trip because Walter has essentially blackmailed her with his knowledge of her affair with a British diplomat (Liev Schreiber), and much of the film's first half is a fascinating portrait of people who absolutely loathe each other but must keep up appearances for vastly different reasons, both related to respectability within their chosen fields (Walter's is science; Kitty's is society). Watts brings an intensity and vulnerability to Kitty that transcends the character's spoiled, selfish origins and shows her as a confused but passionate young woman searching desperately for her place in the world. Even as she makes terrible decisions capriciously, Kitty remains sympathetic and appealing, thanks to Watts' stellar performance.
Norton is more subdued, his character's development more internal, but he does effectively portray Walter's gradual, minimal thawing over the course of the film. The way that Kitty and Walter come to terms with one another is never sentimental or contrived, conveying genuine emotion against the backdrop of turbulent upheaval in China.
Curran previously directed the infidelity drama We Don't Live Here Anymore, also with Watts, and the distance and restraint that hampered that modern story work much better in a period piece. The light overtones of social commentary bring a level of realism but are never distracting, and the result is both sumptuous and satisfying.