cloak-and-dagger behaviour is when people behave in a very secret way, often when it is not really necessary
Usage notes: A cloak is a type of long, loose coat and a dagger is a small sharp knife used as a weapon. In 17th century Spanish theatre, cloak-and-dagger was worn by a dishonest character in the play.
(always before noun)
Is all this cloak-and-dagger stuff necessary? Why can't we just meet in a café like everyone else?