Grace just moved to San Francisco and is excited to start over at a new school. The change is full of fresh possibilities, but it's also a tiny bit scary. It gets scarier when a minotaur walks in the door. And even more shocking when a girl who looks just like her shows up to fight the monster.

Gretchen is tired of monsters pulling her out into the wee hours, especially on a school night, but what can she do? Sending the minotaur back to his bleak home is just another notch on her combat belt. She never expected to run into this girl who could be her double, though.

Greer has her life pretty well put together, thank you very much. But that all tilts sideways when two girls who look eerily like her appear on her doorstep and claim they're triplets, supernatural descendants of some hideous creature from Greek myth, destined to spend their lives hunting monsters.

These three teenage descendants of Medusa, the once-beautiful Gorgon maligned in myth, must reunite and embrace their fates in this unique paranormal world where monsters lurk in plain sight.

Lily Sanderson has a secret, and it's not that she has a huge crush on gorgeous swimming god Brody Bennett, who makes her heart beat flipper-fast. Unrequited love is hard enough when you're a normal teenage girl, but when you're half human, half mermaid like Lily, there's no such thing as a simple crush.

Lily's mermaid identity is a secret that can't get out, since she's not just any mermaid - she's a Thalassinian princess. When Lily found out three years ago that her mother was actually a human, she finally realized why she didn't feel quite at home in Thalassinia, and she's been living on land and going to Seaview high school ever since, hoping to find where she truly belongs. Sure, land has its problems - like her obnoxious, biker boy neighbor Quince Fletcher - but it has that one major perk - Brody. The problem is, mermaids aren't really the casual dating type - when they "bond," it's for life.

When Lily's attempt to win Brody's love leads to a tsunami-sized case of mistaken identity, she is in for a tidal wave of relationship drama, and she finds out, quick as a tailfin flick, that happily-ever-after never sails quite as smoothly as you planned.