Having survived the Horror of Fang Rock, the Doctor and Leela resumed traveling through space and time.  Along the way, they picked up a new companion named K-9.  Here is the rest of the fifteenth century, which began in a British lighthouse and ended on Gallifrey.

The Invisible Enemy (1977, directed by Derrick Goodwin)

This the one where K-9 makes his first appearance.

As a story, The Invisible Enemy is no great shakes.  The Doctor (Tom Baker) and Leela (Louise Jameson) materialize on a spaceship that has been infected by a sentient virus.  Everyone, except for Leela, gets infected.  The virus wants the Doctor to lead an infection of the entire universe.  When the virus orders the Doctor to kill Leela, he breaks free from its control.  He and Leela go to a space medical center, where Prof. Marinus (Frederick Jaeger) uses Leela’s natural immunity to help create a cure for the virus.  At one point, the Doctor and Leela are cloned and the clones are injected into the Doctor to fight the virus.  It’s a fantastic voyage for all.

Prof. Marinus’s assistant is a boxy robot dog named K-9 (voice by John Leeson).  Since Marinus has to go back to Earth, he gives K-9 to The Doctor and Leela as a gift.

How you feel about K-9 says a lot about how you will feel about the remainder of Tom Baker’s time as the Doctor.  Some fans consider the introduction of K-9 to be the show’s jump the shark moment.  A lot more, myself included, have always liked K-9 and view him — along with the sonic screwdriver — as being an essential part of the original show’s charm.  Love him or hate him, K-9, who come figure out any puzzle and who could shoot a loser from his nose, became one of the most recognizable symbols of the Tom Baker years.

Image of the Fendahl (1977, Directed by George-Spenton Foster)

The Doctor and Leela are drawn back to modern-day Earth, where scientists, witches, and cultists are all being influenced by skull that is estimated to be at least twelve million years old.  The scientists assume that the skull is human but actually, it’s the skull of a Fendahl, a race of psychic vampires who developed on the legendary “Fifth Planet.”  The Time Lords tried to destroy the Fendahl but one escaped in the form of a skull.  It first killed all the life on Mars.  (But what about the Ice Warriors and the Pyramids?  Doctor Who continuity rarely added up.)  Then it landed on Earth, where it influenced human evolution to create a race that it could use to its own advantage.

Image of the Fendahl feels like a spiritual descendant of The Daemons, with the same emphasis on rural British atmosphere and paganism (Leela teams up with a white witch) but without the assurance of UNIT waiting on the sidelines to take care of the threat.  Image of the Fendahl, with its suggestion that humanity was specifically developed to be food, is considerably darker than The Daemons and Tom Baker, so often criticized for playing up the humor of the Doctor’s character, gives one of his more serious performances.  When one of the scientists who has been possessed by Fendahl seeks to kill himself and bring an end to the threat, the Doctor hands him a gun.

Image of the Fendahl is yet another Doctor Who serial in which the main threat is revealed be the result of the Time Lords meddling.  The Fourth Doctor spent a lot of time cleaning up Gallifrey’s messes.

The Sun Makers (1977, directed by Pennant Roberts)

The Doctor, Leela, and K-9 materialize on Pluto, where they discover that colonists and workers are expected to pay exorbitant taxes to the Company or risk being exiled to the Undercity.  The Company’s tax collector is the Controller, who turns out to be a quivering mass of seaweed.

The Sun Makers is Doctor Who at its most satirical, poking fun at the British tax system.  Apparently, the original script was much more pointed in its attacks on the Inland Revenue services but the BBC, being the BBC, demanded that the script be watered down.  In human form, the Controller still clearly resembles Denis Healey, the then-Chancellor of the Exchequer.

The Sun Makers is Doctor Who at its most straight-forward, an enjoyable diversion from the more serious episodes.

Underworld (1978, directed by Norman Stewart)

The TARDIS materializes on the R1C, a spaceship that has been on a millennia-long quest to find a missing ship that was on its away to Minyos 2 and which contained the genetic files of the original Minyans who lived on Minyos 1.

This is another story where the Doctor has to deal with the bad decisions of the Time Lords.  Before adapting their policy of non-intervention, the Time Lords meddles in Minyan evolution and the end result was that the Minyans viewed the Time Lords as gods and the Minyans also used all of the Time Lord technology that they had been given to fight a civil war.  The Doctor feels a responsibility to help the crew of R1C complete their quest.

The R1C eventually ends up going through a space nebula and crashing into a planetoid, where they discover the ship they were searching for.  The crew of the ship is being used as slaves by the Oracle, a super computer.

Underworld is one of the more boring of the Fourth Doctor’s serials.  The story feels slapdash and the idea of a supercomputer was a well that the Doctor Who had already gone to far too many times.

The Invasion of Time (1978, directed by Gerald Blake)

The Doctor returns to Gallifrey and assumes his position as President of the Time Lords.  He also seems to go through a total personality change, exiling Leela and announcing that a group of psychic aliens known as the Vardans will be the new masters of Gallifrey.

Leela, even after being exiled, is convinced that this is all a part of some plan on the Doctor’s part and it turns out that she’s right.  The Doctor is only pretending to be allied with the Vardans so that he can discover the location of their planet and put them into a time loop.  What the Doctor does not realize is that the Vardans are themselves being used by the Sontarans, who are planning on invading Gallifrey.

In retrospect, it seems inevitable that the 15th season would end on Gallifrey.  It also seems inevitable that the Sontarans would eventually try to invade Gallifrey.  The main threat of the Sontarans has always been that they are so stupid that they will try to invade any planet.  The most surprising thing about this serial is that Leela stays behind on Gallifrey so that she can marry Andred (Chris Tanchrell), the head of the Citadel Guard.  The idea of Leela living with the Time Lords has been responsible for a lot of fan fiction and it does seem unfortunate that the show didn’t do more with the idea.

Louise Jameson had already decided to leave the show and originally, Leela was to die while fighting the Sontarans.  This was changed because it was felt Leela’s death would be too traumatic for younger viewers.  Instead, the younger viewers were traumatized by K-9 announcing that he would be staying on Gallifrey with Leela and Andred.  Luckily, for them, the final shot of the fifteen season was The Doctor looking at a crate labeled “K-9 Mark II” and smiling.

Little did the Doctor suspect that the quest for the Key of Time was waiting in his future.