The Infinite Sea by Rick Yancey

Following the events of The 5th Wave, the world is in ruins after multiple alien attacks have wiped out most of humanity. Cassie Sullivan, the main protagonist, is trying to survive and protect her younger brother Sam, while grappling with the loss and trauma from the first wave of destruction.

As she and her group hide from the alien "Others," new threats emerge—especially the creation of "Silencers", human children altered by the aliens to hunt other humans. Ringer, a fierce and determined fighter in the group, becomes a key focus in this installment as she infiltrates an alien training facility and uncovers disturbing truths about the enemy’s real plan.