Of his three half-brothers, Somarled and Brusi were not unwilling to give Thorfinn a share of the Orkney jarldom.  For they were meek men, especially Brusi; and, when Somarled died, though Einar wanted two shares for himself, and fought to retain them, he only wearied out his followers and alienated them by his cruelty.  They, therefore, went over to Thorfinn in Caithness.  More important still, Thorkel Amundson, “the properest young man in Orkney,” did likewise, and was thenceforward known as Thorkel Fostri, foster-father to Thorfinn, whom he aided at every crisis of his career.

When Thorfinn grew up, he claimed a third share of Orkney, and, not getting it, “called out a force from Caithness” where he mostly lived.[5] Brusi and Einar then pooled their share of the islands, Einar having the control of both; and Thorfinn got his trithing,[6] managing it by his men, who collected his scatt and tolls under Thorkel Fostri, whom Einar plotted to kill.  Einar next seized Eyvind Urarhorn, a Norse subject of distinction, who had caused his complete defeat in Ulfreksfirth in Ireland, but was sheltering from a storm in Orkney, and killed him, to the great anger of the Norse king.

Grasping at once the opportunity thus created, Thorfinn determined to turn it to his own advantage.  He sent Thorkel to King Olaf in Norway to seek protection for himself against Einar, and Thorkel came back bearing an invitation to Thorfinn to visit the Norwegian court, from which the jarl returned as much in favour with the king as Einar was in disgrace.  Brusi then tried to reconcile Thorfinn and Einar, and Thorkel was to be included in the settlement.  Thorkel, however, after inviting Einar to a feast in his hall at Sandvik in Deerness, a promontory south-east of Kirkwall, discovered a plot by Einar to attack him by three several ambushes as they left the house.  In a striking scene, the Saga tells how Thorkel, wounded, and Halvard, an Icelander, dispatched Einar at the hearth of the hall; how Einar’s followers did not interfere; and how Thorkel fled to King Olaf in Norway, who was much gratified by the death of Einar, the slayer of his own friend Eyvind Urarhorn.[7]

On Einar’s death, Brusi tried to get two-thirds of the isles, but Thorfinn now claimed a half share, and King Olaf, in spite of a visit by Thorfinn to him in Norway, ultimately awarded Brusi two-thirds, Thorfinn having the rest.  Brusi, however, being unable to defend the isles from pirates, about the year 1028 gave up one of his trithings to Thorfinn on his undertaking the defence of the isles,[8] for which a powerful fleet would be essential, and Brusi died in 1031.