stratagem

all the stratagems you've worked out are rendered void.

Knit your brows and you will hit upon a stratagem.

That you have used every ruthless stratagem to win the much-coveted promotion hasn't endeared you to your rivals.

But when the forbidden months are past, then fight and slay the Pagans wherever ye find them, an seize them, beleaguer them, and lie in wait for them in every stratagem (of war);

to devise a cunning stratagem

to employ a clever stratagem

to outsmart the enemy with a stratagem