The Prometheus Design

Summary
From the back cover: Captain Kirk and his crew are on a mission to investigate the mysterious wave of violence that has overtaken the Helvans - revolutions, mass riots, horrible tortures. But this chaos is all part of an experiment by an unimaginable power that soon grips even the crew of the Enterprise...

Captain Kirk is plagued by violent hallucinations and removed from command. Spock takes charge but his orders seem irrational - even cruel.

Unless the terrible power can be stopped, not only the Enterprise, but an entire galaxy will be ensnared in the deadly grip of...

The Prometheus Design.