Frank and Joe investigate the disappearance of Cyril Bayard, a shady investment counselor who's been dating the boy's aunt Gertrude and to whom she entrusted her life savings. His clerk has just been found murdered, and it looks like the bullet was meant for Bayard. The boys visit his house, but he's gone and the place is trashed.

When Aunt Gertrude is fingered as the chief suspect, the Hardy's have to act fast. They head for Manhattan to call on Bayard's business associates. But before they know it, they're drawn into a treacherous chase through a world they know nothing about -- the dark underside of Wall Street.