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.

Trapper and Hawkeye seek to keep a new nurse from being transferred by Hot Lips, and they vie for her affection. Henry Blake, challenged by another commander to a boxing tournament, makes Trapper fight a big, intimidating soldier in exchange for keeping the nurse at the 4077th. Hawkeye and Ugly John employ the use of a glove soaked with ether to insure Trapper's victory, which impresses the nurse. Margaret and Frank's attempts to unfix the match collapses, as they are flattened by the unconscious boxer!

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.

John Hodges, a chopper pilot referred to as The Cowboy because of his gun holster belt and cowboy hat, has been hit in the shoulder, and arrives at the 4077th. He is expecting a letter--he's worried his wife Jean at home is leaving him for another man ("She's probably off with some rodeo rider; she's a sucker for a 10-gallon hat!"). He wants to go home, but Henry refuses, stating Cowboy's wound isn't serious enough to merit a stateside ticket. Bad luck then follows Henry Blake like the seat of his pants: he gets shot at while golfing, his tent gets flattened by a driverless jeep, and the latrine explodes while he's inside. The Cowboy offers to fly Henry to Seoul and then threatens to shove him out! The letter finally arives for Cowboy, assuring he is loved. Hawkeye and Trapper uses the radio to convince The Cowboy to spare Henry's life and come down, at which they succeed.

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.

Frank throws his back out whilst spending the evening with Margaret, and ends up in traction. He promptly applies for the Purple Heart, having been 'technically' wounded at a frontline unit. Tommy Gillis, an old friend of Hawkeye's, is writing a book about the war, and pays him a visit. Later, Tommy is brought into the camp, seriously wounded, and Hawkeye can't save him. A 15-year-old kid is in the hospital to have his appendix out. He joined up to be a hero back home, but Hawkeye has him sent home, giving him Frank's purple heart.

The camp tunes into the Army/Navy football game, only to be shelled and have an unexploded bomb land in the middle of the compound. They ring around trying to identify the bomb, and the camp prepares for the worst. Hawkeye and Trapper are left the task of following instructions to disarm the bomb, which turns out to be full of propaganda leaflets from the CIA.

Hawkeye and Frank argue over Frank's surgical ability. Hawkeye performs a difficult operation and the patient does not recover, as he should. Hawkeye begins to doubt his ability and moves out of The Swamp. He decides to open up his patients again, and discovers a nick in the colon that even Frank admits anyone could have missed.

Captain Kaplan is to be shipped home, but becomes paranoid that something will happen to him before he leaves. He takes the wheel of the jeep to drive to Kimpo himself, but crashes and ends up in plaster. Henry's wife is in labor and gives birth while he has Radar calling the hospital every 5 mins.An entertainer, Jackie Flash, visits the camp to entertain the troops.

A brawl at Rosie's Bar puts Rosie in the hospital, and the 4077th doctors are pressed into service as temporary saloon-keepers. Meanwhile, Father Mulcahy is apprehensive that his long-pending promotion to captain will again be denied. Potter: "The Pentagon. Weird looking building. Four walls and a spare. Monument to Murphy's Law."