Assassin By Accident by E.J. Russell

If a megalomaniacal earth mage kidnaps your little sister, do you:

A) Kill him
B) Kill him
C) Kill him
D) 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 shift
B) He can’t swim
C) He can’t drink
D) 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.