After learning that Vorus, the leader of the guardians, was misusing his power, Tyrum had him brought before him. He questioned him as to his aims and revealed his wish that Vorus would be removed from his post. Angered by this, Vorus declared that he would resist and civil war broke out between Tyrum's men and the guardians.
When Vorus' agent, Kellman, was captured and revealed that the Cybermen were invading, Tyrum convinced Vorus that they had to work together. Tyrum was then shown a rocket that Vorus had prepared called Skystriker. Tyrum allowed the Fourth Doctor fifteen minutes to rescue Sarah Jane Smith from the Nerva Beacon before the rocket was launched, much to Vorus' annoyance.
As his final act, Vorus launched the rocket and Tyrum stood watching as it was successfully redirected away from beacon by Commander Stevenson. The beacon itself missed Voga thanks to the Doctor's actions. (TV: Revenge of the Cybermen)