Nisse is 11 years old and his mother has just passed away. Before she died she gave Nisse a lizard named Harry. It turns out Harry can talk and that he's in fact a small, funny fire-breathing dragon. Harry takes it on himself to help Nisse get a dragon heart. It's almost Christmas and everything just reminds Nisse of his dead mother. She used to love Christmas and now when she's gone all the christmas cheer just makes Nisse angry and sad. Harry helps Nisse handle both school and Christmas. When his unemployed Dad does something really stupid The Dragonheart is put to trial, will Nisse be strong enough to handle it?