a real world point of view
The Cartmel Masterplan was a term invented by fans and popularised by Doctor Who Magazine that very roughly described the overall "vision" script editor Andrew Cartmel and his cadre of writers, including Marc Platt and Ben Aaronovitch, had for re-introducing mystery and general darkness into the character of the Seventh Doctor in the waning seasons of the 1963 version of Doctor Who.
The "plan" — although Marc Platt has called it "more of a mood and direction" than a detailed plan — would have dropped hints of the Doctor's actual origins throughout the later part of Sylvester McCoy's tenure as the Doctor. Due to the show's cancellation and John Nathan-Turner's occasional tinkering with scripts, however, very little of the "masterplan" was ever seen on screen. The "plan" was largely left to play out in other media and was an especially profound part of the Virgin New Adventures range in general and the novel Lungbarrow in particular.
Purpose and origins
The overall plan for Cartmel was to reveal that the Doctor was some form of a reincarnation of The Other, a mysterious figure from Gallifrey's past who helped form the Time Lords' society and perfect the time travel technology of the Time Lords. An early draft of Ghost Light, set, at this stage, not in Gabriel Chase on Earth but the Doctor's ancestral home on Gallifrey, was planned as the lead-in to this reveal but the script was shot down by series producer John Nathan-Turner. Cartmel's plans were later incorporated into the Virgin New Adventures series, to which Cartmel and other writers from the late McCoy era contributed, paying off in the final New Adventure novel to feature the Seventh Doctor, Lungbarrow. Lungbarrow had as its origins a proposed early draft of "Ghost Light". The earlier version of "Ghost Light", in turn evolved into a new story and the new story into the novel.
At some point before 1992 Cartmel, Aaronovitch and Platt sat down and gathered their ideas about Gallifrey. These were passed onto then-New Adventures editor Peter Darvill-Evans, who incorporated them into a Doctor Who writer's guide. 
Seasons 25 and 26
Seasons 25 and 26 several included hints toward this new direction. Some were included in the broadcasts and some were not:
- The Doctor appears to make a slip of the tongue discussing the Hand of Omega with Ace, saying, "... and didn't we have trouble with the prototype", then sheepishly amending this to they when pressed. (TV: Remembrance of the Daleks)
- The Doctor explicitly says to Davros that he is "far more than just another Time Lord". (TV: Remembrance of the Daleks) The scene was deleted from the original BBC broadcast reportedly because John Nathan-Turner objected to portraying the Doctor as a god in case it caused offence. Some regions, including Canada, broadcast the episode with this scene intact.
- Lady Peinforte claimed knowledge of the Doctor's actions during the Dark Times of early Gallifrey, well before his assumed birth date as gathered from the Nemesis statue. (TV: Silver Nemesis)
- When Peinforte is told that the Doctor is a Time Lord, she is seen to shake her head, no, before replying. (TV: Silver Nemesis)
- Control says of the Doctor that he does not fit any description of any alien species. Given that Light's mission was to catalogue all life Time Lords would presumably be catalogued. (TV: Ghost Light)
- Morgaine identifies the Doctor as Merlin, the wise sage and mentor to King Arthur, suggesting that the Doctor would become Merlin in a future story. (TV: Battlefield)
An unfilmed scene from Survival was to feature the Master challenging the Doctor's identity and true nature. The Doctor would argue that we must all "evolve" in some way. This scene was cut when it appeared that the series had come to an end. Rather than finishing the series on such an inconclusive note, the production team decided to go with a different ending scene.
Planned Season 27
Had a twenty-seventh season been developed, Marc Platt's Ice Time would have revealed that Ace had been trained by the Doctor to become a Time Lord, her rebellious attitude helping to reshape Gallifrey's policies and role in the safeguarding of time and space. This is mentioned by the Doctor to Ace in PROSE: Set Piece and Lungbarrow. Something roughly similar happens in the online original story Death Comes to Time.
Ice Time would also have introduced a petty criminal from the 1960s whom the Doctor would help. Following Ace's departure, a subsequent story, set in the 1980s, would have this character's daughter, an aristocratic cat burglar, join the Doctor as his new companion. The intended finale of this twenty-seventh season was to have been Alixon, a story which may or may not have seen the Doctor regenerate into his eighth incarnation and the departure of McCoy.
Andrew Cartmel added further aspects of his ideas when he started writing comic strips for Doctor Who Magazine, beginning with his debut story, "Fellow Travellers" it which it is revealed that the Doctor has maintained contacts with humans on Earth for years and has purchased a house there. The more sophisticated and mature Virgin New Adventures line made the Doctor a more morally ambiguous, unreadable character who had extensive powers and an unknown history. Fans nicknamed the Doctor in his period as "the dark Doctor" or the "arch-manipulator". The novel Lungbarrow, the final Seventh Doctor novel, written by Marc Platt revealed the Masterplan in detail.
The TV Movie
- The TV Movie seemingly sums up the Masterplan, although not in the same way that Lungbarrow does. It features the Doctor saying that he is half-human, a statement that caused much controversy among fans. Cartmel said he in no way intended for that to be the summary of his Masterplan and preferred Lungbarrow's depiction to the TV movie's.
- There is also much debate about how truthful the Doctor was, when making this statement.