Idiom
catch someone in the act (of doing something)
Theme: CATCHING
to catch a person doing something illegal or private.They know who set the fire. They caught someone in the act.I caught Tom in the act of stealing a car.
Idiom
catch someone in the actcatch (someone) in the act
to discover someone doing something wrong.I was trying to clear up the mess on the carpet before anyone noticed it, but Isobel came in and caught me in the act.