Arnold's Christmas is the first ever half hour episode and holiday special of Hey Arnold!.
When Arnold recieves Mr. Hyunh's name in the boarding house's annual Secret Santa draw, he decides to make it the most special Christmas ever for the lonely boarder, and tries to reunite Mr. Hyunh with his long-lost daughter. Meanwhile, Helga agonizes over what would make the perfect present for Arnold.
The boarders assign each other a Secret Santa, and Arnold has to get a present for Mr. Hyunh. He hears his story about his lost daughter Mai, and decides to search the city for her.
Arnold attempts to locate Mai Hyunh through government records, but is rebuffed by the city archivist, Mr. Bailey. Eventually he and Gerald work out a deal; they do all Mr. Bailey's Christmas shopping and he will give him the information. They nearly complete the list, but fall short in getting a pair of Nancy Spumoni snow boots. Without the critical item he refuses to give the boys any information about Mai.
Meanwhile, Helga searches the city frantically for a perfect present for Arnold, but is unsuccessful due to his fixation on to complete Mr. Bailey's shopping list. Learning of the final item she rebukes his quest and faith in Christmas. However, when given a pair of the popular snow boots by her mother, she is able to get Mr. Bailey to search the records through an impassioned speech on Arnold needing a Christmas miracle.
On Christmas Day, Arnold is downtrodden over not getting Mai and her father back together. Mr. Hyunh as a result has no secret Santa present, and is understanding, but depressed. At that point the door bell rings and Phil answers it, only to find Mai Hyunh. Mai comes in and is reunited with Mr, Hyunh. Standing in the snow, far out of sight, Helga wishes Arnold a Merry Christmas, after Gerald tells Arnold that perhaps a "Christmas Angel" was looking out for him.
This is one of the most acclaimed episodes of the show, and it remains a fan-favorite many years after its debut. It is often considered one of the best and most emotionally powerful episodes in the entire series, and is also regularly included in listings of the best animated holiday episodes or specials.