Full of anticipation, ten-year-old Emma goes on vacation to her grandma Dolly in the country. Once there, however, the girl learns that old Klipperbusch has died - and his money-hungry nephew Albert is already in the process of converting the inherited estate for profit. And anything he can't use for this is thrown out without further ado. At least Emma manages to save Klipperbusch's beloved mare Mississippi from the slaughterhouse at the last minute: she persuades her grandmother to buy the horse from Albert. Emma is now a proud horse owner. She is all the more surprised when Albert turns up at her door one day and desperately wants Mississippi back. It's clear to Emma and her friends that this guy can't be up to no good...