When her absent-minded inventor father suddenly remembers that he has five sisters, nine-year old Harriet Bean, who has never heard of them before, determines to find her unknown aunts so that the unfinished family portrait can be completed.

Harriet is invited to help her detective aunts, Thessalonika and Japonica, investigate serious cheating in the world of horse racing. Initially excited by this prospect, Harriet quickly begins to regret getting involved. Will Harriet overcome her fears and find out who is causing Mr Fetlock's horses to lose all their races? Hold on tight for this bumpy ride!