A gang of crooks rob a train. Scotland Yard's Superintendent Mungo suspects Little Walter.

Little Walter's gang, comprising his girlfriend Bikini, Willy the poet, gambler Squirts, Spanish Lorenzo and strip club habitué Specs, are summoned to a meeting. Walt suggests that until the heat is off they stay on an island he has bought off the coast of CornwallThe crooks take up residence in an empty Monastery there, wearing habits and working like monks, to avoid police detection. Bikini is the cook, Willy feeds the pigs and chickens, Lorenzo grows the onions, Specs the potatoes, and Squirts picks apples and tends the goat. Walt milks the cows.

After an inedible meal, the gang are shown to their cells, with wooden boards for beds. They complain that jail would be better. Walt plans to sleep in the head boy's office with Bikini, but the gang demand that he takes a cell the same as theirs. Walt concedes, and the crooks nickname him 'Father Superior'.

Walt receives a telephone call from a fellow criminal. He announces that the gang are in the market for loot. Soon, London criminals start sending the gang stolen goods to dispose of.

Phineas, a local fisherman, brings a boatload of tourists to the island. Walt tells Phineas that he cannot show the tourists around. He then discovers that Phineas used to be a smuggler, and suggests using his boat to deliver stolen goods to the gang. Phineas agrees. They discover that the tourists have entered the monastery. Fortunately, Willy prevents them from seeing Bikini, who is taking a bath. The tourists leave without further trouble.

Phineas sends his granddaughter, June, to buy a dress in Newquay, and then brings in the first batch of smuggled goods. Opening a bag marked 'tulip bulbs,' he discovers fur coats instead. He hides one for himself. June, on her way to the bus stop, discovers Willy stuck on a boat in the harbour. She helps him ashore. Later, she offers to teach Willy how to row.

Phineas delivers the goods to the island. When the gang discover a fur is missing, they give Phineas a friendly warning.

In the Monastery, the gang melt down gold, make stolen furs 'kosher', and forge banknotes. Two genuine monks, Father Septimus and Brother Lucius, arrive to thank Walt for buying the island. The gang try to maintain their disguises, but Walt offers Septimus a cigar, and peppers the conversation with cockney slang. Septimus hopes to visit again. He says he will pray for them. Walt is touched.

Squirts buys Bikini a cookbook in town, and then steals a copy of the Sporting Life. He notices that his greyhound, Gorgeous Geoff, is running that Saturday. Squirts decides to find a betting shop, but Willy, returning after a day spent with June, interrupts him.

While Phineas sleeps, June rows to the island with a bag marked 'Urgent Medical Supplies,' unaware that the bag contains the stolen Montez diamonds.

Squirts asks Phineas to place a £100 bet on Gorgeous Geoff. The local barman puts the bet through to Newquay.

The gang begin to enjoy their daily farm work. Willy becomes seriously ill with pneumonia. Walt prays for him in the Monastery Chapel. The next morning Willy is better.Meanwhile, Superintendent Mungo hears from a tout that someone in Newquay keeps betting £100 on Gorgeous Geoff.

Walt announces that the gang can return to London, where they will divide up the money. Everyone is disappointed, since they have come to enjoy island life. The gang pay Phineas a bonus and ask him if Willy can marry June. Phineas reacts furiously, so they take him to the cells. Walt waves goodbye to June and Willy as the couple leave by rowboat. Walt agrees to marry Bikini, who insists on Walt going straight.

Mungo arrives in town. The barman tells him about Phineas' bets and his work for the monks.Meanwhile, the gang arrive on the mainland, wearing civilian clothing and carrying the loot. Septimus and Lucius are waiting for them on Walt's instructions. Walt hands Septimus an envelope. Police arrive to arrest the gang. Septimus opens the envelope. He discovers that Walt has left Septimus' Order the deeds to the island.