Valentine's Day is usually filled with cards and candy, but this year it is filled with a puzzling mystery. Nate the Great absolutely hates anything mushy, so he is not exactly thrilled when he discovers a giant red paper heart taped right to his dog's house. Who could have left Sludge a secret valentine message? Determined to put an end to the mushiness once and for all, Nate sets out to crack the case. The investigation takes a surprising turn when he learns that his friend Annie is actually missing a valentine of her own. Suddenly, Nate has two cases that might just be connected. With his trusty canine partner by his side, the young detective must gather clues, question his friends, and untangle a web of holiday secrets. Readers will enjoy putting the pieces together as Nate discovers that a little bit of kindness and friendship might not be so bad after all.