Doctor Who: The Deadly Assassin (1976)

It is a testament to the pivotal role of the "companion" or "assistant" in Doctor Who's winning formula that the programme got to its 88th story without the Doctor adventuring on his own.

Having left Sarah Jane Smith on Earth at the end of The Hand Of Fear, the Fourth Doctor (Tom Baker) is 'summoned' home to Gallifrey by a prophetic vision of the assination of the President Of The Time Lords.

In quick time, The Deadly Assassin draws The Doctor into a murder mystery and a web of political intrigue that gives us more information in a single story about the background and mythology of the Time Lords than we had yet been exposed to.

For the first story set on Gallifrey, Robert Holmes' script is bursting with fan-friendly continuity minutiae - the type classification of The Doctor's TARDIS, the Celestial Intervention Agency, the Seal of Rassilon, Cardinal Borusa and the number of regenerations a Time Lord has, as well as the return of The Doctor's nemesis, The Master (Peter Pratt).

It's just a shame then that a large portion of this excellent story - from the end of the second episode through the entirety of the third and into the start of the fourth - is padded out with cut-price surreal imagery as The Doctor enters The Matrix/APC net to fight The Master's protégé (whose identity isn't at all difficult to guess from the moment he enters the story, virtually cackling and twirling a pantomime moustache).

Even if we take it that the iconography of the Matrix is constructed by The Master from his intimate knowledge of The Doctor's psyche - gained from stolen data files - it is still too Earth-centric (clown, samurai, bi-plane, big game hunter, World War I soldier, trains etc) in its imagery and goes on for way too long.

Which is a shame because the three episodes that are not dominated by The Matrix sequences are superb examples of Doctor Who at its best (as long as we ignore The Master's rather sudden and ridiculous escape at the end of the story as well).

A pivotal story in the development of The Doctor's background, in some ways it's a shame that Russell T Davies has wiped Gallifrey from the galactic map in the regenerated Who mythos and we won't be revisiting this potential source of fascinating stories again (except, maybe, in flashbacks).

With modern effects technology, and writing sensibilities, just imagine what a trip in The Matrix would now look like now...