blow (one's) cover(redirected from blew their cover)
blow (one's) cover
To expose one's true identity or motives after they had been intentionally concealed (i.e. after one had been "undercover"). The spy fled when he realized that someone had blown his cover. I totally blew my cover when I stupidly wore my school jacket to steal the other team's mascot.
blow someone's cover
Sl. to reveal someone's true identity; to ruin someone's scheme for concealment. The dog recognized me and blew my cover. I didn't mean to blow your cover by calling out to you.
blow one's cover
Inadvertently give away one's secret identity, as in Mary came to the annual meeting pretending to be a shareholder and hoped no one would blow her cover . This expression uses blow in the sense of "expose or betray," a usage dating from Shakespeare's day.