Paradise Down by Donna B. McNicol
(C'Mon Inn Mystery Series Book 1)
Aloha Nicholás! But will this be a hello or a goodbye?
When Lucia Santerez returns home to Hawaii to help her brother Nicholás with his new dive shop, she learns Nicholás has disappeared--and someone doesn't want him found.
Enlisting the aid of hunky vacationing firefighter, Brandon Matthews, gets them the wrong kind of attention. They discover what lies under the water off the coast of the Hawaiian island of Kaua`i could make you rich or get you killed.
A variant of this story was previously published in Amazon Kindle Worlds.