Star Trek: The Original Series - Errand of Vengeance
Star Trek: The Original Series – Errand of Vengeance is a trilogy of Pocket TOS novels written by Kevin Ryan and published by Pocket Books in . It follows the events of the five-year mission of the Original Series, told from the point of view of a Klingon infiltrator whose mission is to kill Captain Kirk.

The story continues in the Errand of Fury trilogy.

Novels 
 The Edge of the Sword
 Killing Blow

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Errand of Vengeance