Miles cannot wait to spend his summer with his grandma and cousins at their family cottage at High Lake. With Nash, Owen, and his best friend and lakeside neighbour, Ellie, Miles is looking forward to catching fish and eating s'mores and solving mysteries. After all, there is always a mystery to be solved at High Lake. Little did Miles know that a mystery would present itself before his family even has time to unpack their car upon arriving this year!

With the help of a big boat's wave, Gramma's dockside table is knocked into the water, and with it go many treasures, including her lazulite necklace. Miles and friends jump to the rescue, picking up as many spilled goodies as they can muster, but the necklace is nowhere to been seen. Alas, the mystery of Gramma's lazulite necklace begins.

Join Miles and the gang as they uncover clues and follow their hunches in the Mystery at High Lake. Will they be able to recover Gramma's favourite jewels?