After a failed attempt at racing a homemade billcart, Harriet's younger sister Kat becomes obsessed with speed. Kat is determinded to take part in a billcart derby, but her parents will only allow Harriet to drive in it, as Kat is still too young.

 

Harriet — pushed willy-nilly into the scheme — is terrified of getting behind the wheel again. On racing day, however, Harriet proves she's no chicken after all. She starts enhoying herself... until her crazy little sister manages to cause a big upset and gets Kat into trouble once more.