at the mercy of somebody/something

at the mercy of someone

 and at someone's mercy
Fig. under the control of someone; without defense against someone. We were left at the mercy of the arresting officer. Mrs. Franklin wanted Mr. Franklin at her mercy.
See also: mercy, of

at the mercy of

1. Also, at someone's mercy. Subject to the power of, helpless against, as in The captured rebels were at the mercy of the army commander. [Late 1500s]
2. Without any protection against, as in On top of Mount Washington we were at the mercy of the elements. [Late 1600s]
See also: mercy, of

(be) at the mercy of somebody/something

not be able to stop somebody/something harming you because they have power or control over you: Small businesses are completely at the mercy of the banks these days.The little ship was at the mercy of the storm.
See also: mercy, of, somebody, something

at the mercy of

Without any protection against; helpless before: drifting in an open boat, at the mercy of the elements.
See also: mercy, of