They had been able to keep their dark secret to themselves.

For from early on, he was living with a dark secret.

He had come around often enough to know our dark secret.

As are most people who like to keep deep, dark secrets.

Only his parents know the truth about us, and they have kept it a deep, dark secret.

But there is a dark secret in her past that he has yet to learn.

There was a dark secret to the store's success, however.

What she was to him remained a deep, dark secret, even to himself.

And I don't think it was to learn some deep dark secret that one of your patients might be telling you.

A dark secret is revealed about him in the last book.