This appears to be the right book!  At the bottom of each page is a word, which turns out to tell you a drop location under one of the docks.  You send Jiles to go swimming, and he finds a sealed tube under the dock.

What he finds in the tube is shocking.  It turns out that the spy discovered that one of Sofia and Tybalt’s aunts is trying to dig up magical dirt on the twins to get Sofia dethroned.  Technically this aunt would get the throne if Sofia didn’t have a viable daughter (which, at current, she does not).

The Aunt’s name is Sarina, according to this spy.  And the spy says she discovered what Sarina was digging into, magically.

Sarina had to abandon her proof when she abandoned her post, but her notes here say that she is on her way inland, hoping to meet up with Tybalt’s allies.

This is all information that you are sure that Tybalt does not have, and if you send him the information, text me what you send him.

AND THEN THE GAME CAN CONTINUE!