"What does he say about the secret investigation?"

More than a dozen years of secret investigations would be moved any moment through space to the discs in this computer.

But actually, I'm doing a secret investigation for the Crosleys.

Like a phantom of the night, he had come to the circus grounds to begin a secret investigation of his own.

That secret investigation and its disturbing context were the crux of Spin's report.

"This is a case in which secret investigation was the issue."

And finds herself the sole witness in a secret federal investigation.

He must have foreseen, I reflected, the secret investigations of his premises.

Jane then begins a secret investigation of his own to track the killer.