With Jeff laid up in a hospital bed with one arm and one leg in plaster (having fallen off a balcony whilst trying to apprehend a safe-cracker), Marty visits and seizes the opportunity to tell him about a spy drama that he handled while he was still alive — the details of which he has never previously revealed — involving a corrupt MI5 official and spy ring, the details of which he had never revealed before.
While Jeff was out of town, Marty was hired by Major Brenan, a man pretending to be Sir Basil Dougan, a top MI5 official at a country club to retrieve "stolen" important documents from a perceived unloyal member of the British Secret Service. However, the morning after Marty and his hired Liverpudlian safecracker (who also personally steals a diamond necklace) successfully locate the documents, it turns out to be an actual theft from the real important member of MI5. Marty, in disgust, tries to hunt down the imposter Major Brenan and eventually locates him in the sauna of the country club where Marty is forced into an overheated sauna with his suit on (underneath the robes) to attempt to avoid capture from the imposter's henchmen.
Despite this, Marty escapes and later overpowers one of the imposter's leading henchman who attempts to kill him in his car. Marty slams on the brakes smashing the henchman's head against the window, later tying him up in his apartment.
Marty tracks down the imposter's registration number and shadows him to the docks where the faulty Sir Basil Dougan plans an escape with the stolen documents aboard a ship to a foreign country. Marty is eventually able to contact the BBC via the ship's radio for the police to round up the perpetrators.
This was originally written as a conventional episode, but as Mike Pratt really was injured, it was changed to a 'flashback' involving Marty. Pratt had attempted to climb a drainpipe, after celebrating his 38th birthday a little too well.