cloak-and-dagger

[cloak-and-dagger] {adj.} Of or about spies and secret agents.

It was a cloak-and-dagger story about some spies who tried to steal atomic secrets.

The book was written by a retired colonel who used to take part in cloak-and-dagger plots.

(From the wearing of cloaks and daggers by people in old adventure stories).

Compare: BLOOD AND THUNDER.