While observing a burnt-out supernova, the Enterprise picks up a strange message
transmitted in a 200 year old code. The signal is traced to a nearby planet, and when the ship
arrives it is hit by an energy beam that damages it's dilithium crystals, and makes the crew begin to shrink.
Dr. McCoy discovers that the crew will continue to shrink beyond their ability to
control the ship unless a cure is found.
This episode was written by Paul Schneider, who also wrote 'Balance of Terror' and 'The Squire of Gothos'
for the original series.