Hetty and Robert arrive home after a long break with their son Derek in Australia and Hetty has scarcely unpacked before she gets embroiled in a new case about hidden treasure.

With some reluctance Robert agrees to go undercover to help solve a Big House mystery. The owner of the house has died under somewhat suspicious circumstances.

Hetty is asked by local councilor, Brian Weston to help mediate between the council and his mother, Enid Weston, who refuses to leave her flat that's earmarked for demolition.

Hetty’s hairdresser is having problems with her husband, who's been the subject of an apparently random attack.

Hetty finally has a reply to her advertisement in the local press about seeking her only known blood relative.

Robert’s brother appears at the Wainthropps’ house bearing a large suitcase and the sad story of a missing friend.