It's a Mystery, Charlie Brown (1974)

Plot

Woodstock's stylish new nest mysteriously vanishes, prompting him to enlist Snoopy's detective skills. Embracing the persona of Sherlock Holmes, complete with a signature cloak, deerstalker hat, and a bubble pipe, Snoopy teams up with Woodstock to solve the puzzling disappearance. Together, they embark on a whimsical adventure filled with clues and clever antics as they search for the elusive nest, showcasing the charm and camaraderie of the beloved Peanuts gang.