Sir Finistere was a retired White Knight in the first RuneScape novel, Betrayal at Falador.
During his squireship with the White Knights, the knight he was serving under was captured by the Kinshra along with himself. The knight was killed, but he was offered a place within their ranks as a spy within the White Knights. He took them up on this offer, and for years served the Kinshra secretly. Sir Justrain, a fellow White Knight, suspected a spy within the ranks, but he was unable to identify Sir Finistere as the spy and so left the order in disgrace.
In the year 163, a young girl appeared in the White Knights' Castle and was taken into care. At the same time, the retired White Knights were called back from the Falador Almshouse to help train the peons and squires while the active knights were busy. Rumoured to be the daughter of Sir Justrain, he was ordered to kill her. He first tried by getting Bryant, a peon attached to Squire Theodore, to pick up some extra ingredients of a poison from an apothecary, who warned Bryant of the ingredients' deadly nature, so he was forced to kill Bryant. Sir Balladish, who had been following Bryant, was also killed by Sir Finistere, making it appear that Sir Balladish was the traitor and had killed Bryant and been killed by Bryant.
He tried again to kill Kara-Meir by poisoning her hot cocoa. The matron assigned to look after her decided to drink it instead and died, alerting the White Knights to Sir Balladish's innocence. A trap was set up to catch him involving sending two caravans rumoured to contain treasures but really containing armed guards was conceived, and both he and Sir Erical were given information relating to one of the caravans, while Sir Pallas was cleared as he was deemed to be physically unable to commit the treasonous acts. Sir Finistere got word of both caravans and attacked the caravan leaked to Sir Erical, framing him and forcing him into hiding.
He was ordered to free a prisoner, the Kinshra knight Gaius, from White Knight custody. He did so, killing the guards guarding Gaius.
Sir Erical was eventually tracked down to the Falador Sewers, where the squire Marius, the Temple Knight Sir Tiffy Cashien and the alchemist Ebenezer confronted him, only to find him dead, already killed by Sir Finistere. He trapped the three of them and left them for dead when Sir Pallas appeared, challenging Sir Finistere to a duel. Though Sir Pallas stood no chance due to his infirmity, he bought enough time for Ebenezer to break the trap where Marius wounded the traitor and killed him.