American mystery

It is the school summer holiday, three months after Edie Marble faced off with the eco-terrorists. Grandpa David is unwell and has asked his son, Edie's dad, to bring the family to Canada to see him - possibly for the last time - although he doesn't mention that he's already secretly reached out to Edie. In Toronto, Edie uncovers a dark secret from her family's past that has been buried and seemingly forgotten about, but when Grandpa David starts receiving strange messages from an unknown number, the truth finally comes out. Yet again, Edie sets off on an exciting adventure, this time to discover who has been contacting her grandpa and why. Along the way, she visits Washington DC and the Outer Banks of North Carolina before a dramatic climax in Dartmoor. Can Edie uncover a hidden crime and bring the perpetrators to justice once again?