The thing is, other than these books (Vanguard, Errand series and Cloak), I'm not that familiar with "darker"/"sophisticated" TOS novels, and would love some more recommendations..
I suppose it depends on what sort of thing you're looking for. Errand of Vengeance
has the connections to Vanguard
, and Cloak
has the kind of dark overtones that you would associate with Section 31.
I take it you're after something that goes beyond the "planet-of-the-week" formula, but I don't know if you wanted to delve into politics and intrigue or have more character-driven stories.
Well, basically I'm looking for novels that explore the TOS era / timeframe with a darker look - something that goes beyond "just" what was shown on the series itself, and delves into more complex situations, settings and characterizations - preferably more plotically or military-themed.
I hope this explains it a bit - it's more of a feeling I got when reading Vanguard
, and I was looking to experience something similar (and finding it to date only in the Errand
series and Cloak
Barbara Hambly's Crossroad
is dark in terms of tone, kind of spooky, and features a warped future Federation. Probably my favorite numbered TOS novel.