Debts linger, waiting to be paid. When Colonel Niall Pierce is kidnapped, Jani Kilian is ordered to stay out of it.

Niall may be her best friend, but he is also an officer in the Commonwealth Service and a full human while she is the half-idomeni head of the hybrid enclave of Thalassa—to attempt his rescue would not only call his loyalty into question and endanger his life but increase tensions between the Commonwealth and the alien idomeni. Jani is also facing her own problems.

Outside forces and inner turmoil are menacing Thalassa, and the behavioral changes wrought by her hybridization leave her shaken and concerned about what she is becoming. But when a threat from her own past compels her to join the search for Niall, she comes to believe that an adversary she thought vanquished has returned.

As she and her enigmatic partner Lucien Pascal dodge pursuers and build shaky alliances, she realizes her past and present are one and the same, and dangers she once faced could return to claim her and everything—and everyone—she loves. .