The Battle for Amphitrite

It's been two years since Bridgette Livingston faced Horace on the battlefield--and won. Unfortunately, it has also been two years since Bridgette has set foot in Carletta. Her duties as queen of Selene have kept her away from home. However, that is about to change.
When Alaska's father, King Aenon, is murdered, and the underwater kingdom of Amphitrite threatened, Bridgette returns to Carletta. Temporarily becoming a mermaid, Bridgette begins to navigate the world under the Deselvian Sea and stop the evil forces at work. But sea serpents are not her only worries. Tensions back home in Carletta and abroad in Selene are growing. Soon, Bridgette finds herself in a war on multiple fronts, and when the Prince of Blood returns, Bridgette must decide which of her friends she can trust.