Before long, Mary begins to receive strange phone calls from a mysterious, unknown caller.

There was a faint impatience in her expression for the unknown caller.

She is eager to reveal herself to callers known and unknown.

He was testing his unknown caller, in a very subtle style.

I let my anger build toward the unknown caller.

But suppose he knows there is someone besides my unknown caller who has information that could hurt him?

Never ask the unknown caller for a number.

The unknown caller had hung up at the other end.

An unknown caller claiming to be a lawyer or in law enforcement offers to help you get your money back (for a fee).

We have a male caller, identity unknown, who is demanding to speak with you.