Although it was the final Christmas episode of the series, there was a later episode set on Boxing Day, titled "'Twas the Day After Christmas". Also, the short-lived spinoff series AfterM*A*S*H* presented one more Christmas production set in the series' continuity.
It's Christmas, and there's a truce on. Everyone is preparing for the big Christmas feats for the the nearby orphanage. When the supply line that was supposed to deliver the food gets cut, all of the 4077th band together and donate their holiday care packages--B.J. donates fudge, Nurse Kellye donates Macadamia nuts, and Rizzo donates...pig's feet?
They turn to Winchester to donate, but he offers just a small tin of oysters, despite him having received several large packages marked "perishable" in the last few weeks. Despite constant insults from everyone, Winchester refuses to budge.
We see, though, that Winchester has his own plans: he's bringing all the packages to the nearby orphanage, late at night. When he's caught the orphanage's headmaster, Choi Sung Ho (Keye Luke), Winchester tells him it's part of a Winchester family tradition: on Christmas Eve, they leave an anonymous gift of expensive, handmade chocolates on the doorstep of a needy family. Mr. Ho gratefully accepts the gifts, promising Winchester to keep it a secret.
Meanwhile, the truce is broken when a wounded solider is brought in just as the 4077th is kicking off the Christmas party for the kids. Hawkeye, B.J., and Margaret decide to take the case, and keep it secret from everyone else, lest the holiday spirit be ruined.
The young man is seriously wounded, and both Hawkeye and B.J. are certain he's going to die. After seeing a picture of the young man with his family, B.J. decides to continue working on him, determined to keep the man alive long enough so that he won't die on Christmas Day.
Meanwhile, at the party, Winchester sees Rizzo eating a piece of the expensive chocolate. When Rizzo tells him he got in on the Black Market, Winchester asks one of the orphans if they got any chocolate for Christmas. When the little girl says no, Winchester angrily confronts Mr. Ho.
They go outside (with Klinger overhearing the whole conversation), where Mr. Ho admits he sold all the chocolate. Winchester is enraged, calling him a "parasite", but Mr. Ho explains that the chocolate was so valuable that, on the Black Market, it could buy enough rice and cabbage to feed the kids for a month.
Winchester, stunned, apologizes, realizing, as he says, "It's improper to give dessert to a child who's had no meal." Mr. Ho accepts, and returns to the party, with Winchester going back to the swamp.
As Hawkeye and B.J. continue working, Klinger visits Winchester, bringing with him small samples of all the food at the party. When Winchester asks what the gag is, Klinger says it's not a gag: "It's an old family tradition...one that must remain anonymous."
Back in Pre-Op, the young man is about to die. B.J. is so caught up in the moment, though, he tries to stop Father Mulcahy from performing the last rites, alarming everyone.
B.J. calms down, but wants to keep working, but Hawkeye insists he stop: "Let him go...let him rest." B.J. listens, feeling defeated.
Hawkeye then walks to the clock on the wall, and moves the hands to past midnight, declaring: "Look, he made it." They decide, instantaneously, to fake the death certificate.
Later, they run into Col. Potter and a young Korean boy dressed in a Santa hat. Potter saved the last four pieces of fudge for them, which they use as a toast. As the snow falls, B.J. wishes the rest of them a Merry Christmas.