spying
undercover work

He was a nice guy and fairly experienced in undercover work.

As for the surrounding district, that has involved a certain amount of undercover work.

Times like these are one of the reasons I hate undercover work.

Derek had at one time done 18 months of deep undercover work.

I won't get the grade without undercover work on my record.

You don't live a decade around undercover work without learning the tricks.

Much of his early years on the force was spent in undercover work.

He'd had various jobs, each of which seemed to have included some interesting undercover work.

I did a bit of undercover work for the police here once, got involved by accident and made myself useful.

Their own resources are far too limited for corporate undercover work, they say.