Amy Kathleen Ryan - Sky Chasers (#1-3)

Glow (Sky Chasers #1)
What if you were bound for a new world, about to pledge your life to someone you'd been promised to since birth, and one unexpected violent attack made survival—not love—the issue?

Out in the murky nebula lurks an unseen enemy: the New Horizon. On its way to populate a distant planet in the wake of Earth's collapse, the ship's crew has been unable to conceive a generation to continue its mission. They need young girls desperately, or their zealous leader's efforts will fail. Onboard their sister ship, the Empyrean, the unsuspecting families don't know an attack is being mounted that could claim the most important among them...

Fifteen-year-old Waverly is part of the first generation to be successfully conceived in deep space; she was born on the Empyrean, and the large farming vessel is all she knows. Her concerns are those of any teenager—until Kieran Alden proposes to her. The handsome captain-to-be has everything Waverly could ever want in a husband, and with the pressure to start having children, everyone is sure he's the best choice. Except for Waverly, who wants more from life than marriage—and is secretly intrigued by the shy, darkly brilliant Seth.

But when the Empyrean faces sudden attack by their assumed allies, they quickly find out that the enemies aren't all from the outside

Spark (Sky Chasers #2)
Waverly and Kieran are finally reunited on the Empyrean. Kieran has led the boys safely up to this point, and now that the girls are back, their mission seems slightly less impossible: to chase down the New Horizon, and save their parents from the enemy ship. But nothing is truly as it seems…Kieran’s leadership methods have raised Seth’s hackles— and Waverly’s suspicions. Is this really her fiancé? The handsome, loving boy she was torn from just a short time before? More and more, she finds her thoughts aligned with Seth’s. But if Seth is Kieran’s Enemy No. 1, what does that make her?

In one night, a strange explosion rocks the Empyrean—shooting them off course and delaying their pursuit of the New Horizon—and Seth is mysteriously released from the brig. Seth is the most obvious suspect for the explosion, and Waverly the most obvious suspect for releasing him. As the tension reaches a boiling point, will Seth be able to find the true culprit before Kieran locks them both away—or worse? Will Waverly follow her heart, even if it puts lives at risk? With the balance of power precarious and the clock ticking, every decision counts… every step brings them closer to a new beginning, or a sudden end

Flame (Sky Chasers #3)
Waverly and the other members of the Empyrean have scattered, and their home ship has been destroyed. Their mission to rescue their parents didn't go as planned, and now they're at an even greater disadvantage: trapped with their enemies on the New Horizon, trying to find a way to survive. Kieran has been pulled under Anne Mather’s wing, but is she really trying to make peace, or just using Kieran to build her own power? Meanwhile, Waverly is taken in by a mysterious old man who wants to help her bring Anne Mather down—but the more Waverly cooperates with him, the more dangerous her position is, and the more at odds with Kieran she becomes.

Seth's situation is even worse. After setting out from the Empyrean on his own, with only a vague strategy to guide him, he is a fugitive aboard the New Horizon. He's doing what he can to challenge the power of Anne Mather, but he's badly hurt, and getting sicker.

Will Seth ever see Waverly again? Will his health hold out long enough to help her topple their enemies? And will Waverly find a way to unite with her friends before they all fall? Nothing is sure and every moment is a risk in this explosive finale of the Sky Chasers series.