SNOW QUEEN (Secret Knights #4) by Mary Ting
A curse turned her heart to ice, but only true love can melt it.
Cyrus, the possessor demon lord is dead, but his final battle left Hawaii in turmoil. Hundreds of people are wounded, and the aftermath of a volcanic eruption has kept the survivors busy with the cleanup. Schools are closed and stores are being rebuilt. Life is almost back to normal, except for Ikelia, Eli’s mother.
Eligor, Eli’s father, is still trapped inside the Keeper crystal. Ikelia is unable to free him, so she asks Davin, the head of the Chosen Knights, to travel to her past. He takes her to the moment she first became the Snow Queen in search of the clue she needs. They learn they must go to Kaneana Cave, home to a legend about a Shark Man who lures humans through a smaller opening in the cave and eats them. So Davin rounds up the team. But what they find there might mean the end for Ikelia and the Chosen Knights.