McCloy often used the theme of doppelganger, but in the end of the story she showed a psychological or realistic explanation for the seemingly supernatural events.
Then she was an art critic for International Studio and other magazines, and free-lance contributor to London Morning Post and Parnassus.
In 1946 McCloy married Davis Dresser, who had gained fame with his Mike Shayne novels, written under the pseudonym Brett Halliday.
In the 1950s and 1960s McCloy was a co-author of review column for Connecticut newspapers and in 1950 she became the first woman to serve as president of Mystery Writers of America.
Having read the Sherlock Holmes stories as a young girl, McCloy retained an interest in mysteries and began to write them in the 1930s.
In Goblin Market (1943), reporters for two rival wire services investigate the death of one of their predecessors in a fictional South American country in the shadow of World War Two.
The One That Got Away (1945) explored the psychology of Fascism, postulating that it is rooted in woman hatred, and rejection of a mother's tender care of children.
Another successful work is the eighth Basil Willing novel, Through a Glass, Darkly (1950), a supernatural puzzle in the tradition of John Dickson Carr.