Iron Flame by Rebecca Yarros is book two in the Empyrean series.

I usually have a tough time staying interested in a series, but this is not one of those times. Book two kept me just as interested as the first book (Fourth Wing).

Violet and her friends are now in year two. Her relationship with Xaden is put to the test now that he is stationed at a far outpost. They are only able to see each other once a week because of their bonded dragons. She is working with him to smuggle weapons as they figure out their own relationship amidst secrets and the presence of his ex-girlfriend.

The school has a new commandant who is determined to break Violet. She is pushed nearly to death. New enemies (and one old) are also introduced. Violet is working on honing her abilities while also further developing bonds with her dragons, Andarna and Tairn.

Ultimately, events build to another rebellion and a final battle amongst venin and wyvern. Riders and fliers will need to overlook their differences in order to fight together.