When Clair went searching for the professor,she'd met him outside of time in his TARDIS (disguised as his library) while the doctor,Chris and K-9 were imprisoned by Skagra on his invisible spaceship and torment by his living stone henchmen called Krags. Skagra's plan was to his Saliyavan's ability to absorb minds into his own consciousness with his ability to remove minds into his own-allowing Skagra to merge himself with all the brilliant minds he's stolen with his spheres to create one enormous mind. Upon the revelation the man Claire thinks is the professor is a disguised Saliyavan,the Doctors mind copied within Skagra's giant mind able to unravel the time vortex as both TARDIS's are on course to Shada. He returns Saliyavan to Shada. And leaves everyone at Cambridge precisely as it was in the beginning,the Professor included,before he and Romana depart.
Originally meant to be the closing episode of Doctor Who's 17'th season,a writers strike resulted in the story never being completed and therefore never broadcast-or using BBC terminology transmitted. Tom Baker had to fill in the gaps himself with his own narration for the 1994 VHS release here,included remastered footage left available and that is what you see here. As it stands this is a superb Doctor Who story-full of intelligence,wit and adventure and therefore in the same league as City Of Death from earlier in the season. We actually are never 100% sure of Professor Chronotis's true identity. And the doctor and Romana's encounter with him also reveals a few more tidbits about time lord society that is scattered throughout Doctor Who. As for the humor,one scene stands out in my mind: one where the Skagra's mind sphere pursuing the doctor flies past a men's vocalese street choir singing "Chattanooga Choo- Choo". Despite huge gaps filled in by Baker's clever narrations,one of the finest stories for Doctor Who and Tom Baker's era on the show.