As neither Mark nor any of his subjects dare venture to face the challenger, Morolt, Tristram volunteers his services.

The battle takes place on an island, and, after many blows have been given and received and the end has seemed doubtful, Tristram (who has been wounded by his opponent's poisoned lance) kills him by a blow of his sword, a splinter of which remains embedded in the dead giant's skull.

His corpse is then brought back to Ireland to receive sepulchre at the hands of Queen Iseult, who, in preparing the body for the grave finds the fragment of steel, which she treasures, thinking it may some day help her to find her champion's slayer and enable her to avenge his death.
Meanwhile Tristram's wound does not heal, and, realizing Queen Iseult alone will be able to cure him, he sails for Ireland, where he presents himself as the minstrel Tramtris, and rewards the care of the queen and her daughter--both bearing the name of Iseult--by his fine music.
On his return to Cornwall, Tristram, who has evidently been impressed by Princess Iseult's beauty, sings her praises so enthusiastically that King Mark decides to propose for her hand, and--advised by the jealous courtiers, who deem the expedition perilous in the extreme--selects Tristram as his ambassador.
On landing in Ireland, Tristram notices ill-concealed excitement, and discovers that a dragon is causing such damage in the neighborhood that the king has promised his daughter's hand to the warrior who would slay the monster.
Nothing daunted, Tristram sets out alone, and beards the dragon in his den to such good purpose that he kills him and carries off his tongue as a trophy.

But, wounded in his encounter, Tristram soon sinks by the roadside unconscious.

The king's butler, who has been spying upon him and who deems him dead, now cuts off the dragon's head and lays it at the king's feet, claiming the promised reward.
Princess Iseult and her mother refuse, however, to believe that this man--a notorious coward--has performed any such feat, and hasten out to the battle-field.