In 2271, Spock returned to his homeworld after the five-year mission of the Enterprise, resigning from Starfleet to take a teaching position at the Vulcan Science Academy. Upon his return, he met Sekar, who was preparing to become a postulant in Kolinahr. Though Spock offered to take his leave—the first step of a Kolinahr postulant, to sever all emotional ties—Sekar seemed reluctant and delayed their meeting. It would soon become clear why: despite his Kolinahr training, Sekar opposed the teachings of Surak, and sought to follow the ways of "the Declared"—the Romulans. To that end, Sekar entered the Hall of Ancient Thought after incapacitating its Watcher, and allowed his body to become a recepticle of the long-dead High Master Zakal, a powerful sorcerer from the time of the Vulcan Reformation and an avowed enemy of Surak.
Upon taking Zakal's katra, Sekar became embroiled in a war over his own body. For the most part, Zakal allowed him control in order to pilot the ship and chart its course, but in times of extreme anger, Zakal took charge, using his incredible mind-powers to kill in the most painful ways possible. Sekar was not prepared for the fact that Zakal enjoyed inflicting pain and death - not wishing to truly aid the Declared, but rather seeking revenge against the followers of Surak for deposing him. During the final battle with Zakal's former student Sotek, inhabiting the body of human scientist Keridwen Llewellyn, Sekar refused to aid the High Master, and Zakal ejected the ragged katra of Sekar from his body, scattering it to oblivion. Zakal himself would soon follow suit, destroyed by the sacrifice of Sotek and Dr. Llewellyn, and his knowledge kept out of the hands of the Romulans. (TOS - The Lost Years novel: The Lost Years)