The White Thread (The Gateway Chronicles #3)

Darcy Pennington spent her freshman year agonizing over the sacrifice of her dear friend Yahto Veli, the nark who gave himself to the Oracle to set her free. But when she returns to Alitheia determined to rescue him, she soon comes to realize there's much more at stake than just the fate of her friend.

Alitheia is in turmoil, and a new riddle from the Oracle hangs over their heads. The Six, the alchemist Rubidius, and Prince Tellius must set off on a sea voyage into the realm of a legendary archipelago to try and set things right. The foes they meet along the way are both deceptive and charming, and on board the ship, Darcy's heart and mind feel just as conflicted as the mysteries she has to solve.

Darcy isn't sure if she's prepared for another meeting with the Oracle, but if she wants any chance of saving Yahto Veli, she must try.