Volsung built his estate around the trunk of a tree called the Branstock oak. Its branches touched all that encircled it. Volsung had ten sons, the youngest called Sigmund. He had only one daughter, Signy, who was married against her will to King Siggeir of the Goths. At the wedding, Odin himself came as a guest, in mortal disguise, and thrust a sword in the Branstock oak that only the young Sigmund was able to loose. Siggeir, who had tried and failed to free the sword, offered to purchase it, but Sigmund refused. Siggeir left the Volsungs in anger and plotted revenge. He invited Volsung and his sons to visit him and Signy, and on their way there he had them ambushed in a forest. Each night a wild beast devoured one of the Volsungs. Signy could not help them because Siggeir kept her under watch. Sigmund, the last remaining Volsung, was able to survive only because of Signy's craft and intervention. Brother and sister vowed revenge for the deaths of their father and brothers.
Believing that only a pure-blooded Volsung could aid them in avenging the Volsungs, Signy disguised herself as a gypsy and seduced her brother, conceiving a boy she named Sinfiotli. Sigmund did not realize that the gypsy was his sister. When Sinfiotli reached maturity, Signy sent him to Sigmund to be trained.
When Sigmund and Sinfiotli tried to kill Siggeir, Siggeir captured them and cast them into his dungeon, ordering that they be starved to death. Signy was able to cast a bundle of straw into Sigmund's cell before it was locked; hidden in the straw was Balmung, Sigmund's magic sword. Sigurd and Sinfiotli were able to break free. They killed Siggeir and his men, setting the palace on fire. Signy refused to be saved, however; she told Sigmund that Sinfiotli was his son, and then stepped back into the burning palace.