Briana and Daria Devon are twin sisters who manage a business called Two Mermaids Marine Search and Salvage Shop. Their job involves them doing a lot of scuba diving and investigating the marine life in the ocean. The twin's latest job is to study the sea grass on the bottom of the Gulf of Mexico to determine if the water is badly polluted and killing sea life. The sisters are putting together a report with their findings and a negative report can hurt a lot of businesses.

During a routine dive, Briana comes up out of the water to find herself all alone in the middle of the Gulf. Daria had a toothache so she stayed in their boat while Briana dived. But Daria is gone, along with their boat. A bad storm has hit and there are sharks in the water with Briana. Without knowing what else to do, Briana swims to shore. When she gets near the shore, she is unconscious after getting struck by lightning. A man named Cole De Roca comes to Briana's rescue and becomes her partner in the crusade to find Daria.

What happened to Daria? Why would she abandon her sister all alone in the ocean?

As Briana investigates the disappearance of her twin sister, she finds out that she didn't know her as well as she thought. Daria hid a lot of secrets from Briana and this devastates her. Could one of Daria's secrets be the clue to where she has disappeared to?

BELOW THE SURFACE is a well plotted mystery that had me guessing until its exciting conclusion. The story moves along at a leisurely pace until secrets are discovered. The story reads more like a mystery then a thriller as there isn't any white knuckle suspense but more of a who dun it. The scuba diving scenes were interesting and fun to read about. I found the ending to be satisfying and all of my questions were answered. Overall, this is a nice mystery to curl up with on the beach this summer.