The two brothers are visited by an MI6 agent who tells them of a Dutch agent, 'eighty-six' and a nine-fingered assassin, Charon, who plans to kill a Russian diplomat on British soil. When the two brothers find him dying in a telephone box and hear his last words – "South by south-east". They go to the police and meet DCI Snape and his assistant, Boyle, but by the time they return, the telephone box and the body are gone. After a night being locked up for wasting police time, the brothers investigate his hotel-room. When two men begin searching the room, they escape the hotel and get into a taxi.

The cab, drives them to an underground base and they the head of MI6, Mr. Waverly, who explains about Charon's plan to kill Boris Kusenov, a Russian who is flying to England to buy a painting. The two brothers are then gassed and later, wake up in the office. They head to Tim's job interview at a bank, where a bomb planted in Tim's briefcase goes off. Wanted for armed robbery, they run off.

On the run, they stay the night in a guesthouse and the next day visit a ticket office and find out that the 'Amstel Ijsbaan', a word written on McGuffin's matchbook, is an ice-rink in Amsterdam. When they get back, the residents see the brothers on the news and they end up being handcuffed and held a gunpoint by the manager. The police arrive, but they escape and make their way to Victoria station. Without time to spare, they jump on a train to Dover and befriend a Dutch woman, Charlotte van Dam.

To avoid the police blockade at Dover, the two brothers jump from the train and walk to Dover. They arrive in Amsterdam and go to the 'Amstel Ijsbaan', an ice rink on McGuffin's matchbook. Here, find agent 'eighty-six' and speak to him in the café, he tells them about the 'Villa de Winter' – Charon's countryside house. The brothers speak to Charlotte by telephone and she tells them to meet her in the Flevoland. They take the bus there and spot a bi-plane flies down and opens fire at them.

They hide in a cornfield and the plane flies off. Nick has been injured, so they go to a nearby vet. After removing the bullet and cleaning the wound, Dr. Bloem gives them directions to the 'Villa de Winter'. They catch a glimpse of Charon. Tim sets off the alarm and they are chased by two henchmen, Scarface and Ugly. They hide in a nearby windmill and later, make their way to Amsterdam station. When they spot Charlotte, Scarface and Ugly arrive. They all split off and Nick runs into a nearby theatre. To find safety, he volunteers to for a magic box but the magician is replaced by Scarface.

Scarface tries to kill Nick but MI6 agents burst in and arrest him. The two brothers return to England where Mr. Waverly meets them and clears them of their charges. When they get back to the office, Nick realises that Charon has swapped the auctioneer's hammer for a trigger to a bomb. They rush to Sotheby's auction house as bidding is about to end. They disrupt the auction and Boyle ends up running into the painting, trying to arrest Nick. Later on, Charlotte arrives at their office and Nick works out that she is Charon, however MI6 agents burst in, once more, and arrest her.