Participating in that act, I construct plan (6)
I believe the answer is:
tactic
'plan' is the definition.
(tactic is a kind of plan)
'participating in that act i construct' is the wordplay.
'participating in' says the answer is hidden in the clue.
'TACTIC' can be found hidden inside 'that act i construct'.
(Other definitions for tactic that I've seen before include "Action designed to achieve a specific end" , "An action planned to achieve a specific end" , "Plan, manoeuvre" , "Strategy carefully planned to achieve a specific end" , "Ruse, strategy" .)