TARDIS Travels No.8

Season Eight opens with the TARDIS sitting in the corner of what appears to be the Doctor's third UNIT lab. The central control console has been put back in the ship, and from this point on the emphasis will be on the crucial dematerialisation circuit. A new, fully operational TARDIS turns up at a circus site on the outskirts of Tarminster - that belonging to the Master. The Doctor steals his dematerialisation circuit and tries to use it in his own craft - but it is not compatible. His is a Mark 1, whilst the Master's is a Mark 2.
It appears that if you disguise your TARDIS as another form of transport, it can behave like that form. The Master must have driven his ship away in its horsebox form, otherwise UNIT would surely have found and impounded it.
Terror of the Autons might include the appearance of yet another TARDIS. Was the Time Lord emissary, seemingly floating in mid-air, possibly standing in the doorway of an invisible ship? His appearance is heralded by the materialisation sound, though he just pops out of existence when he leaves (but see Journey 077 below).
The Master manages to get his circuit back after the events at the abandoned RAF base in The Mind of Evil.

Journey 075: Nuton Power Complex, to Axos (1971).
With his own ship trapped on Axos, the Master takes the opportunity to have the Doctor's TARDIS transported down to Nuton from whichever UNIT HQ it is in this week. It is unlikely the Doctor would have left his key behind at the lab, so we must presume that the Master's key can open the Doctor's ship.
As well has having a later model of dematerialisation circuit, the Master's ship must be much more advanced as he refers to the TARDIS as "obsolescent".
The TARDIS can store the power station's entire output quite easily.
Pretending to side with the Master, the Doctor leaves Nuton - using the station's light speed converter to bypass a crucial system.

We get a good look at what the Master's TARDIS looks like in undisguised form - a white cabinet.

Journey 076: Axos back to Nuton Power Complex.
The Doctor hard-wires organic material from Axos into the TARDIS console in order to provide it with time travel capability - or so it seems. He puts Axos into a time-loop and manages to break free - materialising back at the now-destroyed power station. It is suggested that the Doctor actually tried to flee his exile, but the Time Lords have ensured that any flights will automatically bring the ship back to late 20th Century Earth.

Journey 077: UNIT HQ, 1971, to Uxarieus, 2472.
Bizarrely, Colony In Space sees Jo Grant set foot in the TARDIS for the very first time. It seems very odd that she should never have been invited to look inside before this point, considering that she and the Doctor have been working together for many months. You can understand the Brigadier not having any interest in the Doctor's scientific mumbo-jumbo, but not inquisitive Jo.
The TARDIS suddenly becomes active and it dematerialises - travelling to the planet Uxarieus in the 25th Century. (Dialogue says 2472, but the colonists are using a calendar for the year 2471. Maybe it's January 1st and they just haven't got round to changing it yet. Too much home-brew the night before...).
This is the work of the Time Lords. The Master has stolen a file on a doomsday weapon hidden on that world, and they are employing the Doctor to stop him.
The ship does not fade into corporeality as it normally does. It just appears instantaneously - quite literally popping into existence on the planet's barren surface.
The Master's (disguised as an Adjudicator spaceship) does the same. Both ships will pop off in just the same way in part six.
(Despite having worked as an AFM on the show since The Crusade in 1965, director Michael E. Briant simply did not realise that the TARDIS' appearances and disappearances were usually achieved through the 'roll back and mix' filming method).
The TARDIS is moved to one of their dwellings by the planet's "primitive" inhabitants, and is later found by the colonists and brought to their main dome.

Journey 078: Uxarieus, 2472, to UNIT HQ, 1971.
The TARDIS returns to the Doctor's lab, just a few seconds after the Brigadier had watched it dematerialise. It's a good job that the Brigadier moved, as it materialises in the adjacent corner from where it left, where he had been standing. (A correction made by the Time Lords, or the ship itself?).

That's your lot for Season Eight. Season Nine will see the console outside the ship for the last time, and more off-world errands for the Time Lords. Plus, the very first sighting of what appears to be a totally controllable TARDIS...