The four remaining relatives of famed practical joker Henry Russell are brought together to hear his last will and testament, revealing a £50,000 inheritance each if they can all complete a set task completely out of character. The assignments are designed to reflect their greatest shortcomings and test their abilities to adapt and ultimately change for the better. Law-abiding retired army officer Deniston (Alastair Sim), secretly writes scandalous novels until he is given a week to get himself arrested for an actual crime and jailed for exactly 28 days. Haughty Agnes (Fay Compton) must find employment as a housekeeper in a middle-class home and retain her position for a month despite her disdain. Simon (Guy Middleton), a penniless womanising rogue, would have to marry the first single woman he speaks to, such as the cigarette girl at the club he frequents (Audrey Hepburn). Finally, timid Herbert (George Cole) needs to hold up the bank manager he works for with a mask and a toy pistol. Can they all pull it off in order to grab the cash?