In Dark Tide Desiderio is captured by Ondalinians and is rescued by Astrid. Des had no idea of his mother and father being murdered. Astrid soon informs Des about it while rescuing him. In the journey we get a glimpse of his uncle Ludovico. He helps both escape, by loaning them an orca Astrid's dad bought for her mom. While getting Astrid's talisman, Des learns that she can't sing. Soon, Des figures he has feelings for Astrid, and they share a kiss and eventually journey to the Kargjord, where the BFR are located.
Desiderio and Yazeed help make plans on how they should attack and argue about where they should attack. He fights alongside Serafina when they take back Miromara from Portia, Vallerio and Lucia. In the end of the book, he and Astrid are Promised to one another.