Dark Duet is a 1942 spy thriller novel by the British writer Peter Cheyney.

[1] Cheyney had become known for his hardboiled crime thrillers featuring Lemmy Caution and Slim Callaghan, but this novel was his first fully-fledged espionage novel.

[2] The novel is set in wartime London, Lisbon and Ireland.

It was published in the United States with the alternative title The Counterspy Murders.

Two British counter-intelligence officers track a network of German agents which they learn is based out of Dublin.