From end of Casefile #17[1] -- Has Gertrude Hardy found true love at last? That's how it seems when Frank and Joe's aunt meets Cyril Bayard. Then the distinguished-looking stockbroker vanishes, along with Gertrude's life savings. When Bayard turns up dead, the Hardys' aunt becomes the number-one suspect. Entering the shady underside of New York City's financial community, Frank and Joe must outmaneuver greedy Wall Street types. But someone is intent on eliminating the boys before they uncover the truth behind Cyril Bayard's death. The evidence that will reveal the killer's identity is hidden in a missing briefcase. Will the Hardys locate it in time to save Aunt Gertrude?

From back of book[2] -- Frank and Joe investigate the disappearance of Cyril Bayard, a shady investment counsellor who's been dating the boys' Aunt Gertrude and to whom she entrusted her life savings. His clerk has 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 cheif suspect, the Hardys 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.