The Day of Darkness (The Aztecs Episode 4)

The one where the Doctor leaves behind the wife he never married...

One of the many relationships threaded through these four episodes is the rivalry between Ian and Ixta, played with great relish by Ian Cullen. The episode opens with William Russell crawling terribly slowly along the tunnel he's been trapped in by Ixta, eventually to escape the other end, but the two are not done yet. When Tlotoxl leaves Ixta to guard Susan, Ian takes great pleasure in walloping his adversary from behind. However, later on, Ian still falls for the age-old trick of picking up the murder weapon and then getting found with it in his hand (exactly what happened to him in The Keys of Marinus too!).

The Doctor is reunited with Susan for the first time since The Temple of Evil, but amusingly the Doctor hasn't got time to be grateful: "My dear Susan! How glad... I'll tell you how glad I am to see you later on." Hartnell's probably ad-libbed it, but it's just so funny!

The Bride of Sacrifice (The Aztecs Episode 3)

The one where the Doctor makes a hot drink and gets engaged...

It's very clever of Barbara to think on her feet and use Tlotoxl's own bloodthirsty methods against him. When the High Priest of Sacrifice challenges her to save Ian from Ixta's killer blow, she swipes a knife and holds it to his throat, endangering the thing Tlotoxl values the most - his own life. We know that Barbara would never cut a man's throat, of course, but Tlotoxl doesn't know that.

Tlotoxl gets about quite a bit in this episode, as he next pops up in the garden of peace to harass the Doctor. "Oh go away, Tlotoxl!" berates the Doctor, who refuses to let Tlotoxl intimidate him. The Doctor gives this irksome villain very short shrift, which is a joy to see after all the trouble he's caused Ian and Barbara.

The Warriors of Death (The Aztecs Episode 2)

The one where the Doctor inadvertently helps to defeat Ian...

The Doctor is not happy. "Well, young woman, I hope you're satisfied!" he thunders at Barbara. "A happy day for you, hey?" William Hartnell is on fire from the get-go in this opening scene, laying into Barbara with a damning tongue-lashing. The schoolteacher is well and truly told off!

"I didn't think about it," whimpers Barbara, to which the Doctor blasts: "No, that's just it - you didn't think!" This argument is up there with the other great Doctor/ companion fall-outs of The Curse of Fenric and Kill the Moon, except here the Doctor is quicker to apologise. So soon after throwing thunderbolts at his friend, the Doctor suddenly becomes quite tender, holding her close and building up her confidence again by advising her to develop Autloc's belief in her.

The Temple of Evil (The Aztecs Episode 1)

The one where Barbara is mistaken for a reincarnated Aztec god...

Hooray, another script by John Lucarotti! He worked such wonders with Marco Polo, so this script - also an historical adventure - promises to be just as delicately and intricately woven. This is in evidence straight away as Barbara and Susan chat about Aztec civilisation, both its good and bad aspects. These are two characters who know one another well, are comfortable with each other. They are human beings in all three dimensions, and the dialogue the actors is given is light years ahead of what Terry Nation has been churning out these past six weeks.

Barbara's true character is catered for - she is a history teacher, and the Aztecs is one of her favourite periods - while Susan is back to being an intelligent teenager, who has obviously read up on the Aztecs and Cortez in the past. Evidently, so has John Lucarotti.