Barrister Alan Hitchcock is put out to grass by his firm, his wife and his children. A lifetime's work all for nothing. His circumstances lead him to a room at SummerVale, retirement home for the elderly. The last 'lag' he defends tells him a story about the perfect job he never got to do. 'H', as the lawyer is known, can't get this story out of his mind while adjusting to his new life.
At SummerVale he finds a group of like-minded people, discarded, disillusioned, downtrodden but not yet dead. He galvanises these old people into raising their expectations and convinces them that they can have a happy, wealthy retirement if only they can pull off a daring robbery! The scam involves diverting a small plane, landing another in its place and stealing the ill-gotten gains of rich people who use this route to escape paying tax on their money and possessions by smuggling their wealth to a Swiss tax haven.
A robbery without violence, stealing from people who won't go to the police to complain. A robbery by O.A.P.'s. Who would ever believe it?