Having just finished the last (sixth) book in this 2-trilogy series, I wanted to write down my thoughts on it while it's all fresh. To start, this is some of the best TOS era series I've come across, providing a darker look at TOS. In my thread about what to read after Vanguard (http://www.trekbbs.com/showthread.php?t=172324), I mentioned this series, and after having read it I can easily say that this is IMO a "proto-Vanguard". The thematic connections with Vanguard are apparent – from looking at the TOS timeframe through other characters (though naturally EoV/EoF feature the Enterprise crew prominently), to looking at the UFP / Klingon relations (and with the Gorkon connection – though this is what probably prevents this series to be IN continuity with VAN). The first trilogy, Errand of Vengeance, is easily the better of the two IMO, with its original premise, captivating characters and surprisingly gripping (at least to me) plotlines. Though it suffers from editorial mistakes (much like the Janus Gate trilogy, its predecessor in the short-lived ST:TOS "imprint"), and these were jarring in several places, the trilogy still managed to be a top notch TOS offering, at least to Trek readers looking for the military / political side of things. The second trilogy, Errand of Fury, while not quite up to the standards set by the previous one, was still a great read – it seamlessly connected the aftermath of EoV to the TOS episode Errand of Mercy, which naturally was the culmination of the UFP / Klingon "arc". I had read about the criticism surrounding the final volume, due to half of it being devoted to the episode novelization, but I think it worked pretty much like intended, and provided the closure needed for the various plotlines. All in all, a solid 8.5/10 – Highly Recommended!