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.