A secret history (or shadow history) is a revisionist interpretation of either fictional or real history which is claimed to have been deliberately suppressed, forgotten, or ignored by established scholars. “Secret history” is also used to describe an alternative interpretation of documented facts which portrays a drastically different motivation or history from established historical events.

A certain type of thriller can be defined as secret history. In such novels, a daring spy, assassin or commando nearly carries out a coup which would have drastically changed history as we know it. Since this is not alternate history but a secret event in our own history, the reader knows in advance that this attempt would be foiled, that all persons in the know would be sworn to secrecy and all evidence be consigned to a top secret archive, where supposedly it still is. Nevertheless, the plot fascinates many readers who want to see how close history comes to being changed (usually very, very close) and exactly how the attempt would be foiled.

Two highly successful novels are considered to have started this subgenre:

Eye of the Needle by Ken Follett: a German spy in 1944 nearly succeeds in foiling D-Day;
The Day of the Jackal by Frederick Forsyth: an assassin nearly succeeds in killing Charles De Gaulle, president of France, in 1963.
These two novels set the framework for many later books: following step by step both the fiendishly clever, competent and ruthless perpetrator in carrying out his design and the equally clever and competent hunter, hot on his heels throughout the book, but who would catch up with him only at the very end. Typically, historical figures – including very famous ones – appear in some key scenes, but are not major actors.

Many other novels of this type followed, most of them with World War II backgrounds. Follet himself published at least two others:

The Key to Rebecca: a German spy in Cairo nearly succeeds in letting Erwin Rommel win at El Alamein.
The Man from St. Petersburg: a Russian anarchist in 1914 Britain nearly succeeds, by assassinating a key envoy of the Tsar, in averting the First World War.
Works of other writers fitting within this type include:

Enigma by Robert Harris: an embittered code-breaker nearly betrays to Nazi Germany the vital and closely guarded secret that the Allies are able to read its secret messages.
The Eagle Has Landed by Jack Higgins: German commandos nearly succeed in kidnapping British Prime Minister Winston Churchill out of wartime England.
The Romanov Succession by Brian Garfield: taking advantage of the 1941 Nazi attack on the Soviet Union, Russian exiles attempt to assassinate Soviet premier Joseph Stalin and restore the monarchy.
The Night Letter by Paul Spike: In 1940, Nazi agents nearly succeed in blackmailing U.S. President Franklin D. Roosevelt into not running for a third term.