"The Adventure of Colonel Nivin's Memoirs" establishes its conflicts in the recent-as-of-the-setting vicissitudes of World War Two, as well as the still-building Cold War. When the episode aired, more recent history involved Watergate and the Vietnam War. The episode, consciously or not, injects some of the issues of 1975 into its 1947 setting.
Now with very few exceptions, cop shows and detective shows tend to draw on an older, more conservative audience. That being the case, you might expect a prime time whodunit examining Watergate-era betrayals in a post-WW2 setting to be muddled in some places, simplistic in others. Unfortunately you'd be right, which is why this isn't one of the stronger stories. Has its charms, though.