Frank and Lu find themselves puzzling through the world of enigmatology, becoming podcasters and investigating a mysterious car accident that killed a young mother.

Podcaster Emilia Belmont lost her mother Leah in a car accident when she was a child, so when she receives an anonymous note telling her to ask her difficult father about what really happened, she hires Frank and Lu to help her.

Emilia's father, Anthony, refuses to discuss the past, so they seek out his old friends and fellow enigmatologists. Frank and Lu's puzzle-solving skills are tested to the max as they track down this reclusive group: Sven, Nerissa and Tom. But their quest takes a deadly turn as the trail leads to four mysterious postcards, a puzzle which unearths hidden treasure.

Can Frank and Lu solve the riddle, find out what really happened to Leah, and unmask a killer?