The TARDIS finds itself near "Traken," and the Doctor (Tom Baker) and his new companion, "Adric" (Matthew Waterhouse), are greeted by an aged guardian who warns of trouble involving “Melkur.” He requests the time lord’s assistance in preventing a looming threat. Upon arrival, they immediately encounter suspicion from the inhabitants, realizing that “Melkur's” machinations have already begun and he has gained support within the ruling council. Throughout this four-part story, it becomes apparent that the Doctor will confront an aged version of his longtime adversary in a battle of intellect. I found Waterhouse to be a good addition as a companion; he offered a scientific perspective and a unique energy to the role, and he interacts effectively with Baker alongside a capable cast to tell a straightforward tale. While lacking extensive visual effects, it manages to feel quite unsettling as it moves toward its unresolved ending. It isn’t among the strongest or most unforgettable installments, but it's still enjoyable.

Source on TMDB