Robert, Katee. Crimson sails series

"The rebellion's fight turns into a battle of the heart in this pulse-pounding conclusion to the Crimson Sails trilogy by New York Times bestselling author Katee Robert. Nox has been steadfastly working as a quartermaster for the rebellion for years. They don't ask for much in return, except for one crucial condition-their ex, the noble Lord Bastian, stays as far away from them as possible. To say things ended poorly between them is an understatement . . . and it's the only relationship Nox has never quite recovered from. But now the rules have changed. Siobhan, the rebel leader, has emerged from hiding to tell Nox that Bastian's involvement in the rebellion has been discovered, and he's being taken captive. The fate of the entire rebellion now rests on Nox and Siobhan's ability to rescue Bastian from the Cŵn Annwn ship. Saving Bastian is only the start of their hardships, as the trio is tracked by ferocious pirates across Threshold. And Nox's complicated relationships and entanglements with Bastian and Siobhan put not only their life at risk but their heart on the line"--