I've given up on my attempt at the Dr Who 'marathon' and am back to watching whatever story I want to watch in whatever order I jolly well please, and this week I've been watching The Invasion.
The Invasion has.... classic Cybermen-in-sewers action, the first proper appearance of UNIT, the debut of the remarkable John Levene, amazing sound effects, Kevin Stoney, aaaaaand one of my all-time favourite bits of Who lore - Planet 14.
But what exactly is 'Planet 14'? Well, that's what I'd like to know!
It is mentioned when the Cyber Planner (a disembodied intelligence representing the Cybermen that communicates with Tobias Vaughn via a sort of electronic thingamybob and thus helps co-ordinate their planned invasion of Earth) tells Vaughn that they know the Doctor and Jamie:
"...they have been recognised on Planet Fourteen. They are dangerous and must be destroyed."
The 'Aliens and Monsters' book remarks Planet 14 is "presumably Telos." But note they are specifically referring to the 2nd Dr and Jamie, and the closest thing they've come to anything that could be possibly called 'Planet 14' is Telos, but in the far future (in Tomb), long after the 1960s/1970s timeframe during which The Invasion takes place.
So there are only two possibilities: it refers to an unseen adventure, or the Cybermen have time travel.
If it's an unseen adventure, that's fairly nice and easy to sort out. It would have helped if the Cyber Planner had given us more details, and when the Dr and Jamie first see a Cyberman they merely react in shock with a gasped "Cybermen!!"... Zoe too merely adds to Isobel that "we've encountered the Cybermen before, we know what they're capable of". So it's entirely possible for Planet 14 to have occurred at any point really between Wheel In Space and The Invasion (or even before it, if the Cyber Planner literally ONLY encountered the 2nd Dr and Jamie, without Zoe.... maybe Victoria was even travelling with them at the time!).
If Planet 14 is Telos, it complicates things.... the Cybermen only 'officially' had time travel from Attack onwards (and it has been theorised that the Earthshock Cybes are in fact time travellers from the Attack era come back in time, hence their computer somehow being able to turn into a time machine that deposits Adric slap bang in the dinosaurs era..... blimey that's complicated).
Grant Morrison has a massively complex theory and relates in The World Shapers (DWM comic strip) that the Cybes actually meet the 6th Dr and (an aged) Jamie on MARINUS and that's actually Planet 14 and that the Voord evolve into Cybermen...!!
If the Invasion-era Cybes have time travel, why are they piddling about with a planned 'physical' invasion of Earth? Why not try and prevent Mondas' destruction again, at the very least? Maybe only one Attack-era Cyberman survived their exploratory time trips and he was only able to bring information (about the future and about the Dr/Jamie) with him rather than a massive Cyber-army?
Who knows??!? (there was an essay about this very subject in the 2nd 'About Time' book, but annoyingly I no longer have a copy)
But in a funny way I don't want to know. Is Planet 14 Telos, the moon, Marinus, Earth in another era, or some other far flung planet we just never got to see? Not knowing gives me that excited little fan-tingle.... :)