At the 4077th Mobile Army Surgical Hospital (M.A.S.H) unit in Korea, two army doctors by the names of Hawkeye Pierce and Trapper John McIntyre receive some exciting news in the mail. Their Korean house boy, Ho-John got accepted into Hawkeye's old college. Hawkeye and Trapper decide to hold a party filled with music, dancing, and alcohol to raise money for Ho-John's plane trip to the U.S. They achieve this by raffling off a weekend pass with a nurse, Lieutenant Dish for R&R in Tokyo.

Frank Burns complains about Hawkeye Pierce's disrespect...and Henry appoints Hawkeye chief surgeon, to Burns's shock. The rest of the 4077th "coronates" Hawk while Frank and Hot Lips complain to General Barker. The General's visit provides him with a view of life at the 4077th M*A*S*H unit: camp hijinks, a poker game, and a surgery session. This shows him M*A*S*H has fun but gets the job done.

Sergeant Baker arrives at the camp with his Moose. Hawkeye decides to find a way of getting her away from Baker. He tries ordering him to release her, tries buying her, and then resorts to cheating at cards. He releases her but she won't go, so he tries to teach her how to be independent.

Henry receives a citation for the camp achieving the best efficiency rating, and then General Hammond reassigns him to Tokyo. Frank then changes the camp to be more military, and he confiscates Hawkeye's and Trapper's still. They use forged passes to go to Tokyo to convince Henry to come back and end up pretending Radar is sick.

A rash of thefts breaks out in the camp. Missing pieces include Frank's silver picture frame, Margaret's hair brush, and Trapper's watch. The camp is searched and everything is found in Hawkeye's locker. Everyone thinks he did it. Hawkeye manages to announce to the camp that the items will be dusted for prints to identify the real thief, and catches Ho-Jon. He needed money to bring his family from the North, and to bribe border guards.

The nurses go to extremes lengths to find a date for Nurse Eddie - they won't go out with anyone until Eddie gets a date. The men draw straws, and Hawkeye is the big loser, especially after Eddie nearly kills him in a scene resembling teenage "mating" rituals.

Hawkeye and Trapper operate on a famous Colonel - after discovering that he is particularly ruthless about sacrificing his men, they come up with a scheme to get him sent back to the states with a little unwitting help from Frank, Margaret, and a drunk Henry.

Brought on by Frank and Margaret's negative reports, General Clayton assigns a psychiatrist, Captain Hildebrand, to examine the 4077th M*A*S*H unit, to see if it should be disbanded. Henry tells them to be on their best behavior, or else they will be split up. But the 4077th soon begins to act in their traditional, insane ways: the shrink experiences Max Klinger, watches the hijinks of Hawkeye and Trapper John, and witnesses the trysts of Frank and Hot Lips. While Hildebrand confronts the unit on its behaviour, choppers bearing wounded begin to arrive and everyone heads for the OR. The onslaught of casualties shows the 4077th's true side.