The flame liquid was a well-guarded secret of a foreign power overseas.

The exact number and identity of the herbs remain a well-guarded secret.

The location was a well-guarded secret - a bit too well-guarded, perhaps.

We work for the United States government and are here to learn why the existence of this facility is such a well-guarded secret.

Particularly within the Music Department, teachers keep the location of trips a well-guarded secret until it has been largely planned.

It is here purely for the public to experience and enjoy, though that is something of a well-guarded secret.

The authorship was for a long time a well-guarded secret.

"The will," Belinda told her, leaning forward as if she were sharing a well-guarded secret.

His birth name, used prior to the attack, has been a well-guarded secret.

During the shooting, the appearance of the "aged" characters was a well-guarded secret.