But no one really knows our part of the story.

But they could only ever know part of the story.

You already knew part of what I was a long time ago.

But you know only part of why I am here.

Each knows his or her own part, but not anyone else's.

"Now we know at least part of what happened to your friend."

She, like the others, already knew part of the answer.

I knew the answer, or at least part of it.

"And now we know the most important part of any such secret."

He knew the answer now, or part of it, at any rate.