Three Cities is a film about three young boys and their love triangle. One is from Beijing, one is from Taipei and the other is from Hong Kong.
The starts starts off of Xia, a young boy, admiring to one day be a writer, an artist and a photographer. Lost and dazed, he meets a young boy over the internet from Beijing, Cal. They start talking for a while, and eventually, Xia starts falling for him as they both explore one another sexuality with each other. Xia then flies all the way to meet each other, where they meet for the very first time together.
Xia returns back home, and Cal eventually starts to ignore him. Xia learns about Cal's old crush, Keng from Taipei and how for so many long years, has tried to win his heart. Cal eventually breaks up with Xia, breaking Xia's heart and Cal leaves him to try to get into a relationship with Keng.
Xia feeling upset, decides to take the risk and starts talking to Keng, spiteful of him for taking away his first relationship away from him. As they begin to talk more, Keng eventually begins to fall for Xia. 2 weeks of talking, Keng ask him to be his date to a school dance, where Xia accepts. He flies to Taipei where they meet for the first time together. Xia lives with Keng for 2 weeks, as they begin to develop more feelings for each other. Keng and Xia makes a promise to one another, to be together again this summer.
While away, Xia leaves to travels to Canada with his parents. On the week he returns home, he leaves to Taiwan, where Keng comes to pick him up, and they live together. As they began to be with each other more and more, they start to become more irritated by each other. Eventually, Xia leaves to visit his mom for a moment, where he meets Cal again, and shares an affair. Cal misses him and tells him that if ever things don't work out between him and Keng, that hopefully, they can be together once again.
Xia then leaves Cal's place, and bikes back home, towards the beach, to Taiwan, saying that he loves Keng now, but will miss Cal.