Sesame Street's 50th year is the perfect opportunity for a music- and memory-filled special for the entire family. It's the biggest celebration ever on The Street, and lots of friends are on hand to share in the fun. But the celebration could be derailed if it's discovered that the iconic Sesame Street sign has mysteriously gone missing. It's up to some resourceful Muppets to try to find out what has happened to the sign and try to get it back without disrupting the festivities.