The Dark Labyrinth by Amy Kuivalainen

Penelope should know that any holiday with the Magicians isn’t going to be normal…

Penelope wants to stay on a boat, diving for whatever is calling to her in the buried remnants of Atlantis. Unfortunately, no matter how much you hate Christmas, breaking a promise to a group of immortals is a bad idea. It’s been months since the battle with Thevetat, and the magicians are still reeling from the losses they suffered. It’s time to come together and celebrate the Winter Solstice in a way only the magicians can.
Alexis decides what they need to heal their hurts is to revive the Atlantean solstice tradition of the Dark Labyrinth, a way to shed the shadows of the year and bring in light for the spring. But magical labyrinths have minds of their own, and when gods get involved, all bets are off.

Please note that this novella contains adult themes, violence, and sex scenes.