Dear Ex follows three people, all linked to one another because of a fourth person who dies before the film begins. Adolescent Song Chengxi (Joseph Huang) loses his father Song Zhengyuan (Spark Chen of band Quarterback) to cancer, but instead of actively mourning him, Chengxi finds himself caught in a feud between his widowed mother Liu Sanlian (Hsieh Ying-xuan) and his father’s gay lover Jay (TV star Roy Chiu). Before his death, Zhengyuan listed Jay as his insurance beneficiary, which enraged Sanlian, making her even more of an overbearing nag than she previously was. Fed up, Chengxi moves out and into Jay’s unsightly flat. Already at odds over love and money, the trio seems poised for further conflict.