In the third book of the Faerie Tales series, the story expands. In the outset story, Fergus, Aoife, and Niamh hunt down the reincarnation of Tamlin so that they might break the curse.
On the inset story, Aoife attempts to find Cu Roi Mac Daire's weakness, so she can use it against him. She finds darker secrets await outside his castle's walls.
Fagan, now going by Fergus, takes up Tamlin's offer to train with the fae warriors so that he might gain favor with Mab. The prospect of ever seeing Aoife again is bleak until the legendary Cuchulainn, Mac Daire's sworn enemy arrives.
(This book is written to stand alone, but reading Warrior Tithe will give you the backstory of the characters.)
If you're a fan of Maas, Black, Armentrout, or Martin, you'll love this take on the fae and legends of ancient Ireland.