The holiday season is usually merry and bright, but a missing piece of mail threatens to ruin the festive cheer. Annie's giant dog, Fang, is feeling incredibly sad, and when Fang is unhappy, the entire neighborhood feels it. Nate the Great discovers that a very special Christmas card sent from Fang's mother has mysteriously vanished in the mail. Even though it is freezing cold and snowing heavily outside, Nate knows he cannot let his friend's dog suffer through a miserable holiday. Bundled up against the winter weather, Nate and his brave dog, Sludge, set out to sniff out the missing envelope. Retracing the mail route through the deep snow is not going to be easy. Young readers will eagerly follow along as Nate uses his sharpest detective skills to crack the case and ensure that everyone has a crunchy, munchy, and truly happy Christmas.