The analyses of a text

The protagonist is one of family members of Amber.
The Pattern is a maze-like shrine and the core of Amber.
If one of family members of Amber goes through the Pattern, he/ she gets some special abilities.
He is going out with Coral, a daughter of the prime minister from a neighboring country Begma.
She want to see the Pattern.
And he thinks she was possessed by a sorceress he knows of.

So, "What is it that you want?" I asked.
"Just to see it. Honestly," she answered.
"No, I mean that if you are what I think you really are, I'm asking the big questions: Why?"
Coral was silent for the space of an audible deep breath, then, "How could you tell?"
"You betrayed yourself in small ways discernible only to one who has recently become paranoid," I responded.
"Magic," she said. "Is that it?"
"It's about to be," I replied. "I could almost miss you, but I can't trust you."
["Sign of Chaos" of The Great Book of Amber by Roger Zelazny]
I'd like to know if "tell" means "know."
And I'd like to know if I can take "what it is" to be implied after "It's about to be."
Thank you in advance for your help.