I motioned Sweetheart to get behind me—which she did, eager to take a hand in one of "father's ploys."
1722, "anything with which one amuses oneself," Scottish and northern England dialect, possibly a shortened form of employ or deploy. Popularized in the sense "move or gambit made to gain advantage" by British humorist Stephen Potter (1900-1969).
A device or stratagem; a move, esp one designed to disconcert an opponent while keeping one's position; a shrewd maneuver
[1722+; apparently fr Scots dialect; popularized by the late British humorist Stephen Potter]