Skullduggery is a 1970 American adventure film directed by Gordon Douglas produced by Saul David and starring Burt Reynolds and Susan Clark.

It is based on the French novel Les Animaux dénaturés (1952) (variously titled in English as You Shall Know Them, Borderline, and The Murder of the Missing Link) by Jean Bruller (writing under the pseudonym "Vercors").

Otto Preminger optioned the stage rights and got Nelson Gidding to adapt it under the title The Case of the Troublesome Topis.

[4] Giddings later said he showed the original novel by Jean Bruller writing as "Vercors" to Otto Preminger with the idea of making a film of the book.

[9] After Burt Reynolds and Susan Clark were cast, Karl Malden expressed interest in playing the role of Otto Krebs that the screenplay described as a fat man.

David had a number of films in development at Universal—A Stretch on the River, Marie Beginning, Dove Creek Rodeo and The Tuck—but none were made.