Sam Allen is a young private detective who investigated the disappearance of Captain Stroman's jade necklace from the Sea Bright with mixed results. He uncovered Arthur Jensen as the culprit and, when investigating the linked theft at Applegate Mansion, managed to fool Frank and Joe Hardy with a simple disguise of a fake beard and reversible coat. However he also managed to raise suspicion by using the alias "Mr. Smith" when questioning Gertrude Hardy about the boys' activities and also got himself kidnapped by Jensen through clumsiness.