计策

That is a capital plan.

plan to lure the enemy in

ruse to gain time

bold stratagem

turn over a ruse in one's mind

fall into the enemy's trap; be trapped by the enemy's stratagem

map/work out a strategy; make a plan

plan/contrive/devise a stratagem

see through sb's stratagem/artifice; penetrate a design

apply/pursue/use a strategy

improve one's plan

change one's strategy

resort to/adopt a stratagem