(1981) The Enterprise receives an emergency call for a not-obviously-urgent prisoner transport, interrupting Spock's investigation of a singularity just as it was showing some worrisome results. Of course it's all related but I won't tell you how except to say that it's a fun time-twisty puzzle. McIntyre delivers just what you want a tie-in novel: she respects the world and characters and brings enough ideas of her own to keep it fresh.