Castrovalva is a story of firsts in many ways: one of the very few stories from the classic series to be a direct follow-on from the previous story (and it must be added, a bit of a risk considering Logopolis ended more than 9 months before), the first story to feature a true regeneration crisis, and the end of the ‘Master’ trilogy. This is also where the fuller expression of JN-T’s stamp on the program began and the ‘supervision’ of Barry Letts and overall influence of Christopher H Bidmead ended. As it ‘should’ be seen, Castrovalva was truly an inflection point for the program going forward. The long shadow of Tom Baker began, and indeed needed, to recede starting now.
The contrast between these two Doctors was stark enough already, but it’s worth remembering that Castrovalva was Davison’s fourth story to go into production. JN-T quite rightly judged that Davison needed a bit of runway to get into the role. Would the Davison era have been wrong-footed from the jump, although not anywhere near to the same extent as happened years later with The Twin Dilemma) if Four to Doomsday, and with Davison very clearly still finding his way, had directly followed Logopolis?
Time to start winding down the Whittaker era, next time.