Obsidio by Amie Kaufman & Jay Kristoff (Illuminae Files #3)
Kady, Ezra, Hanna, and Nik narrowly escaped with their lives from the attacks on Heimdall station and now find themselves crammed with 2,000 refugees on the container ship, Mao. With the jump station destroyed and their resources scarce, the only option is to return to Kerenza–but who knows what they’ll find seven months after the invasion?