Alther Mella left Septimus Heap in mid-flight to go speak with Olaf Snorrelssen and made a comment to Sep on how Olaf was sad that he never made it home to see his daughter. Olaf was also Summoned by Snorri, his daughter, to fight Queen Etheldredda, a Substantial Spirit. At that time, he learned that she is his daughter (a big let-down to him, for he was hoping for a son to continue his legacy as Trader).
He showed himself to Merrin Meredith, only to be regret by doing it. For Merrin went into detail about ransacking DomDaniel's bones for the Two-Faced Ring and disrupted both the living and the dead in their everyday lives.
Snorri met Olaf's ghost when she and her mother Alfrùn were sailing home to the Lands of the Long Nights.