An elderly admiral takes a youth drug to settle an old hostage situation.
Admiral Mark Jameson, a famous and frail Starfleet officer, is brought aboard to negotiate the release of hostages on Mordan IV, where Karnas, the planet's leader, has asked for him personally. Jameson had handled an earlier hostage crisis there decades before.
As the mission goes on, Jameson grows visibly younger. He has secretly been taking an alien rejuvenation drug, which is now harming him. It also emerges that during the earlier crisis he had secretly supplied weapons to both sides of the conflict, fuelling a long civil war, and Karnas wants revenge.
The drug finally kills Jameson, and his death satisfies Karnas, who frees the hostages. The episode deals with regret and the cost of trying to undo the past.