The Enterprise receives an emergency signal from a sector of
space, responding to it. When they show up, they encounter Klingon's,
who have received the same phony signal.
Klingon's are beamed aboard the Enterprise. As they clash, their
futuristic weapons disappear, and are replaced by swords. Numerous
battles break out around the ship.
A strange, alien life form turns out to be behind all this. Laughter
is used to make the alien exit.
Errand of Mercy,
The Enterprise Incident,
A Private Little War