The Crucible books are wrapped around core images, themes and events, and very beautifully written. They are each analyses of the three central characters of Kirk, McCoy and Spock, very ambitious and rather more 'literary' in aspiration than most trek lit texts (including David R George III's other works).
Crucible: McCoy: Provenance of Shadows
Spock: The Fire and the Rose: Spock
Kirk: The Star to Every Wandering