The third, fourth and fifth stories of the twentieth season were conceived by John Nathan-Turner and Eric Saward as a trilogy reintroducing the Black Guardian in the BBC sci-fi drama. Mawdryn Undead The Black Guardian recruits a young man named Turlough to assassinate the Doctor. Although outwardly an ordinary pupil at a boys' private boarding school, Turlough is in fact an alien who believes that the Guardian will return him home if he succeeds. Terminus The TARDIS attaches itself to a space liner after Turlough, still under the Black Guardian's influence, damages its controls. The Doctor and Nyssa meet two space pirates, Kari and Olvir, who have come on board the liner in search of plunder, while Tegan and Turlough get lost in the infrastructure. Enlightenment The White Guardian warns of impending danger and directs the TARDIS to what appears to be an Edwardian sailing yacht, the SS Shadow, but is actually one of a number of spaceships taking part in a race through the solar system, the prize being Enlightenment. Extras: ? Commentary with cast and crew? Who Wants to Live Forever? - cast and crew look back at the making of the story.? Deleted and Extended Scenes? Out-takes? CGI Effects? Photo Gallery? Isolated Score - option to watch the story with the isolated music score.? Coming Soon trail for a forthcoming DVD release.? Easter Eggs? Programme Subtitles  Three interlinked stories from the Peter Davison era of Doctor Who, the Black Guardian Trilogy brings together Mawdryn Undead, Terminus and Enlightenment, as the Doctor finds himself under threat from an old foe. The enemy in question, of course, is the Black Guardian of the title, who first appeared at the end of the Tom Baker Key To Time season. Across the three stories of the Black Guardian Trilogy, he’s a constant background figure, instead introducing and recruiting Turlough to kill the Doctor on his behalf. The three stories introduce Turlough as a companion eventually, but also marks a farewell for Nysaa. Each of the three stories has its merits, although Mawdryn Undead is hard to beat. It helps that it marks the return, after some time, of Brigadier Lethbridge-Stewart to Doctor Who, although by now we discover that he’s a maths teacher. Not for long, though, as he’s soon back into action, in a story that’s one the Peter Davison era’s finest. Terminus and Enlightenment are less successful, but both are still interesting in their own right. The former sees the Tardis landing on a seemingly deserted and out-of-action space station, while the latter, intriguingly, is set against the backdrop of a big race through space. The Black Guardian never really steps to the forefront across the three adventures, it should be noted, and at times his involvement does feel a little forced. But this is, nonetheless, a fine collection of stories, with one major standout among them. --Jon Foster