Reference:Atrus, opening address (Riven)

Thank God you've returned. I need your help.

There's a great deal of history that you should know, but I'm afraid that I must continue my writing.

[Atrus gives you a small book.]

Here. Most of what you'll need to know is in there. Keep it well hidden.

For reasons you will discover, I can't send you to Riven with a way out. But I can give you this. It appears to be a Linking Book back here to D'ni, but it's actually a one man prison. [Atrus hands you another book] You'll need it, I'm afraid, to capture Gehn.

Once you've found Catherine, signal me, and I'll come with a Linking Book to bring us back.

There's also a chance, if this all goes well, that I might be able to get you back to the place that you came from.