Follow clues, solve puzzles, crack the code... find the missing millionaire.   The celebrated museums of the Fairfleet Institute are known for curating the mysteries of humanity. But they don’t solve mysteries. Luckily, twelve-year-old friends Alex Foster and Asha Singh of the A&A Detective Agency do. Or they will . . . once they get a real case to test their skills as sleuths.   When Dr. Alistair Fairfleet, the institute’s eccentric chairman, disappears on the first day of Alex and Asha’s summer vacation, they receive a letter written by the missing millionaire himself inviting them to a game involving complicated clues and puzzles. It is just the sort of case they’ve been waiting to tackle. But nothing in the Fairfleet case has a simple solution. As the kids track down clues, they uncover art forgeries, archaeological crimes, and Fairfleet family secrets. All of this tests their partnership and forces them to confront the complicated legacies of the people and places they admire most.