The first book in Alessa Thorn’s fast-paced modern fantasy series, ‘Mercenaries and Magic,’ is titled “Darkest Night.” The narrative culminates in theft after a seductive start. Kon, a guy whose path once crossed with an enigmatic woman after he stole a mystical artifact from her, finds himself in a similar situation. Raised by vicious mercenaries, Athena Edgeworth is not someone who can be betrayed without repercussion. When they come up against a shared foe, their perilous game of attraction and competition gets more intense. This mature paranormal story promises action, magic, and retribution. It is full of ethically dubious characters, dark comedy, and sultry romance.