The Forever Ship — Francesca Haig

The apocalypse has come and gone, and now every person is born a twin: one a strong Alpha, one a mutated Omega.

The Omegas live in segregation, cast out by their families as soon as their mutation becomes clear. Forced to live apart, they are ruthlessly oppressed by their Alpha counterparts. The only thing that keeps the Alphas at bay is the fact that whenever one twin dies, so does the other.

In this thrilling conclusion to The Fire Sermon trilogy, Cass, Piper, and Zoe have discovered that Elsewhere exists, and it's more real and more complicated than any of them could have imagined. Now, they must race to prevent the Alphas from destroying what might be the only salvation for the Omegas.

The end to their lifelong discrimination is in sight, but before she can be free, Cass must overcome her loyalty to her Alpha twin, Zach, her most dangerous enemy. But if they're not careful, both will die in the struggle for power.