With the end of the school year fast approaching, Grace and Jack are looking forward to what their summer might bring. As a final goodbye to middle school, they decide to take one last trip from their science class, the place where their adventures all began.

What starts out like any other trip quickly goes drastically wrong when they are spotted upon their return to class.

To make matters worse, they discover the mysterious ink is having side effects not only on them, but also on their favourite travel spots. For Grace and Jack, questions are piling up faster than they can answer them as they continue to unravel the mystery of Miller's Island.