The Enterprise is summoned to transport a dangerous criminal from Starbase prison to a rehabilitation center: brilliant physicist Dr. Georges Mordeauxs, accused of promising to send people back in time -- then killing them instead.

But there's more at stake than just a few lives. For Mordeaux's experiments have somehow throw the entire universe into a deadly time warp. All of existence is closing in on itself -- and only Spock can stop The Entropy Effect!