at (someone's) mercy(redirected from at their mercy)
at (someone's) mercy
Under the control of or dictated by the actions of someone else, without the ability to defend or liberate oneself. Please don't report me to the head master. I'm at your mercy! Once the gangsters were able to blackmail Susan, she was at their mercy.
See also: mercy
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.