Each of the episodes of this series featured a special guest star, who would help the gang solve the mystery of the week. Some of these guest stars were living celebrities who provided their own voices (Don Knotts, Jonathan Winters , Sandy Duncan, Tim Conway, and Sonny and Cher, among others); some were dead or retired celebrities whose voicing was done by imitators (The Three Stooges and Laurel and Hardy), and the rest were present or future Hanna-Barbera characters: the characters from Harlem Globetrotters, Josie and the Pussycats, Jeannie, and Speed Buggy all appeared on the show during or after their own shows' original runs; The Addams Family and Batman and Robin both appeared on the show a year before they were incorporated into Hanna-Barbera shows of their ownThe Addams Family and SuperFriends.