Elmo skipped down the street, humming a happy tune. But today, something felt different. The usual clamor of laughter was replaced by whispers of concern. "Why is everyone so serious today?" Elmo wondered aloud.

Big Bird, towering above the others, examined the banner with a puzzled expression. "Who would cover up such a beautiful message?" Ernie scratched his head, thinking hard. "Maybe it's a clue!" he suggested excitedly.

"We need to figure out who did this and why," Elmo announced, his eyes shining with determination. Grover, always eager for an adventure, nodded enthusiastically. "I will use my super detective skills!" he declared.

Bert examined the ground around the banner, his attention to detail unmatched. "Aha! Footprints!" he exclaimed, pointing to a trail of small, muddy prints leading away. Abby Cadabby fluttered nearby, her wings twinkling in the fading light. "And look, there's glitter too!"

Elmo held up a tiny red feather. "I know whose feather this is," he said triumphantly. Zoe, looking sheepish, stepped forward. "I just wanted to surprise everyone with a new message," she admitted. "But I didn't mean to cover up the old one. I'm sorry!"

Big Bird carefully painted a rainbow, while Ernie added a sun. "Let's make it the best banner ever!" Elmo cheered. As they worked, the bond between them grew stronger, the mystery bringing them closer than ever.