Theo's hobby of researching objects found in river silt leads to his solving a half-century-old mystery.Theo-an apparently young teenager with a single mom-has an irresistible narrative voice: sincere, sensitive, funny and conversational. Readers will immediately be drawn in by his reference to "something bad" in his town's history and to rumors of a ghost haunting the bridge where he conducts his river dredging. When he excitedly uncovers an old pocket watch, Theo uploads a photo of it to his social feed and, knowing it's been underwater for decades, jokingly inquires if anyone recently lost it. Although rattled by an anonymous, threatening reply, he is determined to learn the watch's provenance. Is it connected to the young traveler who died by "misadventure" in 1967? Theo's best friend-a blond, freckled girl named Syd-provides a strong, steady complement to his timidity. The pair conduct interviews, pore over old newspaper clippings, and contact a possible descendant of the traveler. Theo's interactions with local bullies are cleverly woven into the storyline. Spoiler alert: In real life, the new evidence plus other revelations should have prompted Theo to urge local authorities to reopen the case. However, that might have created a darker ending-and the conclusion does satisfy. Characters are cued White.An engaging mystery told simply but eloquently. (Fiction. 8-12)