Sinister summer series

Meet the Sinister-Winterbottoms: brave Theo, her timid twin, Alexander, and their older sister, Wil. They're stuck for the summer with their Aunt Saffronia, who doesn't know how often children need to eat and can't use a smartphone, and whose feet never quite seem to touch the floor when she glides-er-walks. When Aunt Saffronia suggests a week pass to the Fathoms of Fun Waterpark, they hastily agree. But the park is even stranger than Aunt Saffronia....

Everything is creepily normal... and that's what's creeping Alexander and Theo out. The Sinister-Winterbottom twins have braced themselves for weirdness, but it's nowhere to be found at Camp Creek. There are friendly counselors, s'mores by the fire, and even a tie-dye cabin. It's the best camp Theo has ever seen! Alexander doesn't feel the same way, though. He's too nervous about fitting in. Until suddenly, he's not. In fact, Alexander's not nervous...

Following the clues left behind, Theo and Alexander find themselves at Siren's Song Seaside Amusement Park, where they must work together to escape, stop their newfound nemesis Essa, save Wil and their friends, and find their parents.