Mirja finds her grandmother's old hat in the attic and sets off singing along the road with it on her head. On her journey, she meets composer couple Theodor and Thea Tekonen and gets a ride from hat maker Kosonen and his son Ilmari, who falls in love with Mirja. However, the girl continues her journey alone and, with the help of the circus troupe leader, gets to perform at Linnanmäki, where Ilmari finds her again.