The biography and plausible account devised for a secret agent for concealment; cover(1940s+ Espionage)
An alibi; a false narrative explanation: We agree on the cover story, that you haven't seen me for three weeks(1940s+)
The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D. Copyright (C) 2007 by HarperCollins Publishers. Cite This Source
Idioms and Phrases with cover-story
A featured story in a magazine that concerns the illustration on the cover, as in The earthquake is this week's cover story for all the news magazines.
A false story intended to mislead or deceive; also, an alibi. For example, Their cover story while investigating local repair services was that they had just bought the house and were having problems, or The suspect gave the police some cover story about being held up.