Page "Vislor Turlough" Paragraph 2

During the course of the next two serials, Terminus and Enlightenment ( collectively known, together with Mawdryn Undead, as the Black Guardian Trilogy ), Turlough finds himself unable to decide whether or not to carry out his assignment from the Black Guardian, but eventually rejects him in favour of loyalty to the Doctor.

Although always slightly cowardly, with excellent instincts of self-preservation and a streak of ruthlessness, his relationship with the Doctor and Tegan improves with time ( Nyssa having departed at the end of Terminus ).

He is one of the few companions capable of operating many of the TARDIS's systems, being able to run a diagnostic in The Five Doctors and program the TARDIS to retrieve the Doctor in Planet of Fire.

Initially expressing a desire to return home, he continues travelling with the Doctor and Tegan until Tegan leaves at the end of Resurrection of the Daleks.