Rapid aging afflicts all six colonists on Gamma Hydra IV and five members of Kirk's six-man landing party - all but Chekov. With the Neutral Zone so close, suspicion falls on the Romulans testing a new weapon, but is it? With time running out, answers are elusive. As Kirk's memory progressively deteriorates, regulations necessitate a competency hearing no one wants - the outcome of which may eventually lead the Enterprise to its destruction with all aboard.