Big Bird and Snuffy are the hosts of "The Letter of the Day Show" on Sesame Street! The only problem is that the letter they were supposed to introduce and sing about is broken into two straight pieces. Big Bird and Snuffy need help determining which letter it is, so they use the guests on the show as clues. Their first guest is a box, which begins with the letter "B", so they think the letter must be "B". When they try to put the broken pieces of the letter together, however, it does not form a "B". Big Bird and Snuffy realize the letter must have two straight lines. The next guest is wax, so Big Bird and Snuffy think the letter must be "W", but that letter has four straight lines. The next guest is Leela dressed up as a Tyrannosaurs Rex. Big Bird thinks that this has all become too hard because all of the guests start with a different letter - box, wax, and Tyrannosaurs Rex. After he says the words out loud, Snuffy realizes that all of the letters end with the same sound. They figure out that these words don't start with the same letter, but end with the same letter-"X"! Leela helps them cross the two straight lines of the broken letter together and they form the letter "X"! Other guests that end with the letter "X" appear on the show and they all sing a song together!