John is a 19-year-old man just arrested for murder. The police found him sitting on the floor of a public bathroom, with red origami cranes spread around him, staring at a man he'd just shot. It's London in the 1990s. John is arrested and descends into mental torture as he slowly breaks from reality during his incarceration.
In retrospect, the audience sees how John arrived in such a position. He is half Chinese, half British, a dichotomy further exacerbated by his being a closeted gay man. John's is a story of self-acceptance. He works at his dad's restaurant and has a budding academic career at Cambridge, but John's internal struggle with himself is seeping into his ability to function. He starts hooking up with men in public bathrooms, but he is unwilling to admit that he's gay.
As John becomes more frustrated, he starts seeing Dr. Jack Worthing, a shrink. Dr. Worthing helps John work through some stigma and make steps toward self-acceptance and reconciliation. Still, John is overwhelmed by self-loathing, hating both his gayness and his Chinese heritage.
When he meets Tom, an investment banker, John quickly develops romantic feelings which, at least temporarily, seem to outweigh his fear and hatred. John and Tom strike up a brief relationship, visiting each other and hooking up, but eventually the reality of Tom's own self-hatred comes crashing into John's idealization of his lover. They start a heated argument while "cottaging" one day, which ends with John losing his grip on reality and shooting Tom in the chest.
