Tension mounts , however , when Harry is mysteriously chosen by the Goblet of Fire to compete in the dangerous Triwizard Tournament , even though another Hogwarts champion , Cedric Diggory , was already selected . Tension mounts , however , when Harry is mysteriously chosen by the Goblet of Fire to compete in the dangerous Triwizard Tournament , even though another Hogwarts champion , Cedric Diggory , has already been selected .