Elixir (Covenant, #3.5) by Jennifer Armentrout: First, let me just say I love everything Jennifer writes. I especially loved this short little novella. It was the perfect way to tide fans of the series over till Apollyon comes out and it was wonderful getting a glimpse of this world from Aiden's point of view. I adore his character even more now.
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The Covenant series: Pure by Jennifer Armentrout