Cash - Dragon Heartbeats, #3

Iron is kryptonite to Cash and his dragon shifter clan. He offers to be the guinea pig in a laboratory to help them overcome their weaknesses. Unfortunately, Cash didn't count on meeting a sexy doctor called Carissa. Carissa's no stranger to shifters. Her cousin has hooked up with one of Miami's Everglade shifters. But she has no clue that there's such a thing as dragon shifters. She thinks she's helping out an average, run-of-the-mill wolf, bear, or tiger shifter.
And Cash doesn't tell her his secret. Then again, Carissa's got a secret of her own. Her nephew has been kidnapped. The only way she can get him back is if she delivers the blood of the shifter she's supposed to be finding a cure for.