While studying an asteroid, the U.S.S. Enterprise is attacked by three Romulan vessels which claim that the Federation ship has trespassed into Romulan space. The U.S.S. Enterprise hides from the Romulans in a gaseous energy field to avoid the close range barrage from the war ships.

The gas from the cloud enters the Enterprise's computer systems and affects the functions of the computer. When the ship leaves for repairs the computer proceeds to play practical jokes on the crew by altering various ship functions, so that drinks leak and silverware bends. Spock is humiliated by his own microscope, and Scott is pelted with fruits and pies from a food dispenser. The crew discovers the source of the jokes when outrageous laughter is heard over the intercom. Sulu, McCoy and Uhura are trapped in a recreation room and Scott is unable to fix the logic circuits because gravity has been shut off. Life support systems are replaced by laughing gas, which causes pain to Vulcans.

The ship returns itself to the Neutral Zone, thereby inciting a Romulan attack. The ship then plays a practical joke on the Romulans by creating a balloon-shaped like the U.S.S. Enterprise. Kirk tricks the ship back into the energy field, which is followed closely by the Romulans. While in the energy field the computer is returned to normal but the Romulan vessel begins to be affected by the same symptoms. Kirk decides to wait a bit before telling the Romulans how to remove their practical joker.

Cast:

William Shatner as James T. Kirk
Leonard Nimoy as Spock
DeForest Kelley as Leonard H. McCoy
James Doohan as Montgomery Scott
Nichelle Nichols as Uhura
George Takei as Hikaru Sulu

Guest Cast:

James Doohan as Search Party Crewman
Majel Barrett as Enterprise computer
Lou Scheimer as Romulan Commander
Norm Prescott as Romulan crewman
Majel Barrett as Lieutenant M'Ress
James Doohan as Lieutenant Arex

Creative Staff:

Written By: Chuck Menville
Director: Hal Sutherland