Assassin by Accident. Carnival of Mysteries

If a megalomaniacal earth mage kidnaps your little sister, do you:A) Kill himB) Kill himC) Kill himD) Magically indenture yourself to him to ensure her safe return Welsh water horse Nevan Quirke would have happily opted for A, B, or C, but had no idea where his sister was hidden-so, option D it is. He's not a fool, though. He made sure to limit his obligation to a single task. Unfortunately, he neglected to nail down a few tiny details before the geas brand was seared into his skin, and now:A) He can't shiftB) He can't swimC) He can't drinkD) If he fails, he'll be bound to the mage for eternity Oh, and that task? Assist in an assassination. If only he weren't so thirsty. And if only his partner for the heinous job weren't the most appealing man Nevan has seen in his entire two-thousand-year life. Assassin by Accident takes place in E.
J. Russell's Mythmatched universe and is part of the multi-author Carnival of Mysteries series. Each book stands alone, but each one includes at least one visit to Errante Ame's Carnival of Mysteries, a magical, multiverse traveling show full of unusual acts, games, and rides. The Carnival changes to suit the world it's on, so each visit is unique and special. This book features grumpy/sunshiny, hurt/comfort, mistaken identity, opposites attract, unexpected derring-do, and of course an HEA-no matter how little the men in question think they deserve it.