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

But when Mordreaux escapes, bursts onto the bridge and kills Captain Kirk, Spock must journey back in time to avert disaster -- before it occurs!

Now there's more at stake than just Kirk's life. Mordreaux's experiments have thrown the entire universe into a deadly time warp. Spock is fighting time ... and the universe is closing in on itself with the relentless squeeze of ... the entropy effect.