London, 1950. A bank robbery is led by the self-styled George 'The Great' Brain [Sid James] that steals about £50,000. The robbers slip away in a hearse, disguising themselves as undertakers, and are chased into the countryside. George manages to hide the money — a briefcase full of cash — in the trunk of a hollow tree just before all three are arrested. The heist lands them a fifteen-year sentence at Wormwood Scrubs.
Fifteen years later, upon release in 1965, the trio returns to the spot where they left the loot, only to find the landscape transformed into a new town with a housing estate built around the tree. The tree now sits precariously inside the grounds of the local police station. George and his gang move into a nearby house, renting two double rooms on the first floor and presenting themselves under false names: Mr and Mrs Hook, Mr Line, and Dr Sinker (allegedly an ornithologist). They also take up residence with a widow and her daughter — Dot Franklin [Wanda Ventham] and Sally Gamely [Edina Ronay] — who live in the same house and watch the tree from their windows. To keep up appearances, George reluctantly agrees to marry his longtime girlfriend Myrtle Robbins [Sylvia Syms], who isn’t keen on a quiet life but would rather he settle down than chase the loot.
Their plan to recover the money begins with observing the tree using a seaside telescope that costs a penny every five minutes. They first try to steal a ladder to scale the wall, but someone steals it back. Next, they attempt to haul the tree with a harpoon and rope, and then scheme to tunnel under the wall. Dr Sinker’s room swap with the landlady allows access to a lower floor, but the entire sequence is chaotic and undermined by their own incompetence. Meanwhile, the women living in the house devise their own scheme to seize the fortune, and they manage to pull it off — only to discover the money has been shredded by mice nesting inside the hollow tree.
In the end, the criminals’ persistence collides with fate, leaving a twist of irony: the sought-after cash has vanished in a way they never anticipated, trapped within a tree that has become a symbol of their failed plan and their long-awaited chance at a new life.
